There has been a lot of talk about the value of prospects relative to veterans. It seems that prospects are hard to come by at the moment, with many teams attempting to re-build. Here is one example on how values change throughout a career. I know it's an imperfect, and perhaps flawed, study, but bear with me.
Season 15 Round 1, Pick 1
Durazo was a legitimate #1 overall pick. He projected (from memory) to the high 80s low 90s overall, with high 70s/low 80s contact, power, and vs lhp, and mid to high 80s vs RHP and batting eye. He also projected to be a plus baserunner and had excellent intangibles. In the field, he projected to a plus 1B and marginal LF. Clearly, he was one of the top (if not the top) rated positional player and was the object of many re-building eyes. As a prospect, only one other type would bring more value, an elite (#1 overall draft pick or $30 million plus IFA) SP (think Ivy Latham as a prospect)
He played his first two seasons in Philly prior to being dealt to Durham. He was not injured and put up good numbers, so his value as a prospect was about as high as possible.
At the start of Season 17, he was traded from Philly to Durham for
J.R. Beckett. This was a classic top prospect for elite ML SP deal. Beckett was 30 and at the peak of his (potential) Hall of Fame career (2 Cy Young's, 4 all-star appearances at the time) and Philly had designs on the World Series. It is unclear if Philly had a chance (or thought that he had a chance) to re-sign him after the season.
Beckett would go 19-6 and win the Cy Young for the division winners before filing for free agency and signing a near-max deal with Washington. Philly would receive two picks for Beckett in the Season 18 draft, which would become Joshua Duffy and Benny Rivera.
So, before Season 17, Durazo was worth one season of a Cy Young SP and Type A compensation (anywhere from a #1-#4 rounder and a supplemental #1).
In the middle of Season 17, Durazo was traded from Durham to Boston for Aaron Simon and Tomo Yosida.
Both Yosida and Simon were SP prospects picked in the middle of the first round. Simon projected to a top of the rotation guy (low 80s overall), and Yosida to a border-line #2 (high 70s overall). Yosida was eventually traded to Hartford and is 82-79 with a 4.20 ERA in his ML career. Simon would go 48-31 for Durham before being traded to Montreal. He is 79-48 with a 4.08 ERA over his career.
So, in the middle of season 17, a still elite position prospect was worth two very good (mid-first round) SP prospects.
Durazo would spend 4 ML seasons in Boston, winning Rookie of the Year and making his only all-star appearance in Season 19. At the end of his Boston career, he had just signed a 5 year, $8.5 million per deal. So his transition from prospect to ML player was complete.
In Season 23, he was traded from Boston to Milwaukee for Ken DeRosa. At the time, Durazo was in the first year of his 5 year deal and still only 26 years old. Additionally, due to his 98 patience rating, he would likely never file for free agency. In other words, as long as Detroit wanted him, they could have him.
Durazo would bat .301 with an .858 OPS in his only season for mtorabdaddy. DeRosa is poised for his ML debut next season and will likely be a star. It will be interesting to see which one has the better career. As you can see, Durazo still had an incredible amount of value on the trade market at this time.
So, a young, controllable, elite position player was worth, basically, a younger version of himself (top 5 in the 1st round position prospect).
In Season 24, he was traded from Milwaukee to Philadelphia for Pasqual Cruz and Peter Scanlan. Still controllable and still young at 27, Durazo began his decline in value here.
Cruz was a $15 million IFA SP prospect and Scanlan a supplemental first round RF prospect. I would equate a $15 million IFA SP to a mid-1st round SP.
So, in Season 24, Durazo could command one mid 1st round SP prospect and one supplemental round position player prospect. In one season, he had gone from having the value of a younger version of himself, to being worth a mid-1st round SP and supplemental position player. Since he was worth two mid-1st SP's in Season 17, clearly his value had declined by this point.
Cruz was eventually traded to, of all places, Durham for Travis Gibson, Chin-Feng Itou, and Jose Casilla. Scanlan has yet to find a place in the majors. Durazo would hit 41 homers and steal 60 bases in 1.5 seasons in Philly.
In Season 25, Durazo is in the process of being traded from Philly to Durham for Posiedon Lueke and Melvin McCormick. Lueke is a bottom half of the Top 10 in the 1st round position prospect, and McCormick a bottom of the 1st round/supplemental SP/RP. I would argue that his value in Season 25 is about the same as his value in Season 24.
As you can see, Durazo certainly had more value as a prospect than he does now - and he was much more valuable as a 26 year old than as a 27 year old. But why? His decline in value began as a 27 year old in the 2nd season of a 5 year deal. His ratings have not declined, he has not been injured, and he is likely to hold his ratings for a long time and re-sign as long as the team will have him. The likely conclusion is an obvious one - as an elite player gets closer to 30 and is past the first year of his first big contract, people will pay less for him, but, interestingly, this does not hold true for elite SP's around 30 (see Beckett, J.R. at the top of this post).
Keep this post in mind as you navigate the trade waters. For those wanting to buy, there are great deals for elite players under 30. For those wanting to sell, prospects can be had at a premium, unless you have a true #1 SP to offer in return.
Edited to Add......
Boston just traded Homer Ross (#1 overall draft pick SP prospect) to Houston for SP Geraldo Mendez and C prospect Harry Hernandez.
This deal is close to the first deal made for Durazo. Ross, like Durazo, was the first pick in the draft. Beckett was much better than Mendez (although, Philly just got one year of Beckett whereas Mendez will be in Boston as long as Boston wants him), and the two draft picks would likely be preferable to Hernandez. Mendez was a steal in the IFA market at $10.9 million and he likely would have been drafted in the Top 10 if he had been eligible.
So, in this case, the #1 overall pick SP prospect = 30 year old top of the rotation SP and a supplemental #1 draft prospect.