DRJ....RBs who improve as they get older are EXTREMELY Rare.....and only improve based on system, not skill.
Tiki is the only one who I think his skills actually improved...especially ball control.
This is extremely rare becuase when ur an RB, you have already come to the NFL dance with the skills you have and instinct. The position skill set is smaller, and technique means less with RUN skills, which is our discussion point here (not pass blocking). In contrast, OL almost always build thier technique becasue their position requires more technique and less instinct.....which is why its not a "skill" position. I digress.....anyway...
TJones had health issues and was miscast in the wrong system in AZ. So was Marshall in IND before he was traded to STL in the Edge deal (drafted from MIA, FL). MF nearly caught as many balls as he carried in STL, and like LT2, his fantasy value wasn't from rushing...it was receiving that made him elite.
Can KJ turn around? sure its possible, but not probable. He is also miscast, and would thrive better in DEN, BAL*, or ATl. Zone schemes where RBs are asked to hit a specific hole, and make one cut....this system does not require highly gifted (skilled) RBs with great vision (think Barry, LT2, Dunn when u think vision).
I think KJ is the same type of runner as Kevan Barlow. A hard runner with limited creativity and wriggle. For example, KJ always spins after contact in same direction. It worked great (late '04) till teams had film on him (2005). Both have a running style that looks to run over defenders rather than run by, and their body type doesn't match that, thus injuries. What body type do you need? Think Mike Anderson, TDavis, EDickerson. KJ and KB are tough, but not tough enough to overcome the hits they take because they are not big enough or fast enough or elusive enough.
Both of these guys are best used as backups if not in a zone blocking scheme (which lessens their wear, and maximizes their limited skill). They are good, but not great backs. Fantasy owners have given both of them extra love in preaseason due to being starters, and that love is undeserved.
As for your Faulk-Manning story, its sadly misleading.

Those boys played one year together, Peyton's rookie year. Faulk had to run more to save Manning's bacon. Manning was not the pro he is now, nor was he remotely respected by 1998 defenses. Faulk blossomed the next year under Vermeil in STL, a coach who notoriously perfers quicker, undersized backs like Faulk, Preist, Westbrook, but who are extremely versitile, but weak inside (due to size).
Now, if you want to jump the shark with KJ, you probably already have and voted for him (and owned him in 2005). For dynasty, you'll stubbornly chase KJ just like many did with Barlow. There are few who still believe in Kevan, but they're out there! ..and they prefer to stay quiet. You'll join that army with ur love for KJ. :X
Andre Johnson had a horrible year. But so did every HOU player not named DDavis that mattered. Is he on a decline, not at all. Capers always builds a franchise, then falls apart in year 3-4. This is his MO and his doing, and got him fired again. Kubiak made Plummer look great. Think about what I just said and let it sink in....the work Plummer and Great in the same sentence....but its true.
For DRJ's sake I'll list some true WR busts as he seems unsure of what that really means. For the sake of time and gigabites of space, I'll stick with just first round busts from 1997 thru 2004. To not be a bust, they have to be a consistent, proven starter for 3 years. If its obvious they'll be a starter and are only in their 2nd year, I gave them benefit of doubt (see Fitzgerald, McGahee, LJ). A consistent #3 Wr on their team does not qualify, nor do journeymen.:
TOTAL BUSTS: (20):
Charles Rogers, Reggie Williams, Freddie Mitchell, Rashaun Woods, Bryant Johnson, David Terrell, Koren Robinson, Rod Gardner, Peter Warrick, Travis Taylor, Sylvester Morris, R J Soward, David Boston, Troy Edwards, Kevin Dyson, Marcus Nash, Ike Hilliard, Yatiel Green, Reidel Anthony, Rae Carruth
JURY STILL OUT: (7):
Donte Stallworth*, Ashley Lelie*, Jevon Walker*, Michael Jenkins, Lee Evans, Roy Williams*, Michael Clayton, TAM
* 2005 was only time Donte broke 800 yds. in 4 years.
* 2004 was only yr Ashley broke 800yds. in 4 years.
* 2004 was only yr Jevon broke 800yds. in 4 years. If Favre goes, will he bust?
* 2004 rookie year was only time Roy broke 800 yds, very fragile.
ESTABLISHED STARTERS: (7):
Andre Johnson#, Santana Moss#, Plexico Burress#, Reggie Wayne, Torry Holt, Randy Moss, Larry Fitzgerald#
# 2005 was only time in 3 years Andre didn't pass 800 or 900 yd markers.
# Santana didn't produce anything till 3rd year.
# Plex has been very inconsistent.
# Fitzy didn't break 800 yds last year, but broke out in his 2nd year. Unproven over time, but very promising, and will be starter for coming years.
It should be noted that Roy Williams gets more hype than Andre as does Jevon and others in the "Jury Still Out" category.
WRs are VERY hard to pan, and take more time, and I encourage DRJ to read up or ask a GM to validate. Further, here is the RB pic in the same time frame:
TOTAL BUSTS: (9):
Curtis Enis, Robert Edwards, John Avery, Ron Dayne, Trung Canidate,
Michael Bennett, William Green, TJ Duckett, Thomas Jones*
* TJones is on his 3rd team and probably won't hold off Benson in 06. Look at his numbers, but he is the lone example of improvement after first 3 years.
JURY STILL OUT: (3):
Steven Jackson, Chris Perry, Kevin Jones
ESTABLISHED STARTERS: (11):
Warrick Dunn, Antowain Smith, Fred Taylor, Edgerrin James, Ricky Williams,
Jamal Lewis, Shaun Alexander, LaDainian Tomlinson, Deuce McAllister,
Willis McGahee, Larry Johnson.
Wow. Lesson learned for DRJ. RBs are far more successful and sooner. I only used first rounders because they have the best shot by NFL pro consensus, which is why they went in the first round!
Game. Set. Match.