Adcom 535L upgrades?

I have an old Adcom 535L amp (60wpc) from the 1990s. It's a utility amp and actually sounds decent if a bit grainy in the mids and highs. I'm not going to try to sell it, as it doesn't promise much on the used market. 

I'm wondering if anyone has replaced caps or other key parts in their older Adcom gear and if so whether (a) it made a real difference and (b) how much it cost? 

Musical Concepts/Musical Design may be a rebuild or upgrade path as well. They are not cheap but their work is top shelf. 
I’ve owned a few 535s and they always worked flawlessly and sounded fine. I currently use a later 5300 as a backup/satellite (outdoor speakers) amp and sold the last of my 535s a few years ago. The 5300 is 85wpc and in my humble (!) opinion it sounds far better than a 535, even the later models (5 way binding posts added instead of the twisty things they had originally). I may get the 5300 upgraded someday or fixed if the caps get leaky as it just works as it should. Great torroidal/mosfet amps costing very little relative to how they sound.
The 535i is a well designed amplifier and responds well to upgrades. Do a search and you'll find a good bit of information about upgrade paths. If I remember correctly it was a Nelson Pass design. 
Here's one:
There was an outfit that specialized in upgrading 535i but I'm not sure if there are sill in business. Worth checking.  
I have looked inside. Looks fine. Works fine. I'm in the Tweak-light Zone on this one, for sure!
Have you looked inside the amp? Leaking capacitors etc..? Might just need a good cleaning the 535 while the lowest watt was considered one of the best performance for the money at the time.
Yeah, thanks @oldhvymec 
Appreciate it. I have a buddy who loves audio but can't really afford to do much right now. He's turning 50 this year and likes my Adcom. Either he or my son will get a present from me, and if it's possible to polish a radish for not that much money, it'd probably make a nice gift. My buddy has very decent Paradigm bookshelves and some Schiit gear, including a decent preamp. If it doesn't break the bank for me, seems like a no-brainer.
OP it was 65.00 for parts I did the work. That was a 5500, too.

I would put it on the shelf, UNLES there is something wrong and you want to spend the money..

It's a DIY for sure but having someone do it.. You'll never recover the money.

People can say what they want. A LOT of people used and still do use The OLD and the NEW.. Some are all tricked out.. they can sound very good.. especially for the money.. They do run a little warm.. Actually the warmer the better.. 555 was real popular because you could mono it and get some pretty serious power for the money once again..

@johnss Thanks for the suggestion. I'm probably not capable of DIY on this, but knowing what might make a difference helps a lot. Appreciate it.
those amps usually seemed to have a gritty upper end. was pretty easy fix though. Add some film bypasses to the main filter caps. will cost you about 8 bucks worth of parts if you can  DIY it. Years ago, I used to do upgrades on those earlier Adcoms. The 555 was more work. Adcom put those shiny chrome plated buss bars in the amp to fool some. But the sounded thin and bright. Best thing to do was replace them with solid copper buss bars. Made an amazing improvement. 
@oldhvymec  What do you mean by "shelf it"? Do you mean, don't bother? $65 for caps replacement doesn't seem so bad. Please clarify -- I want to know what you think about my question! Thank you!
Shelf it hilde

I have two stacks of old Adcoms. 565s(4) 5500, 5800 7500 all work as they should.. BUT they are old.. the 5500 cost me 65 to replace all the bad caps.. There are two banks.. Not left and right one in front of the other. Main filter caps and a second set... I don't know what they are called.. They took a dump though.. Great unit, so it the 5800.

The 565s are too if you catch them before the board get messed up because of leaking caps.. darn mess.. Brain does an excellent job on 565..costly though..
A good shop will bring back to like new.

    Where do you live ? A general area anyway.
great shop in Rockford, ILL. 

  THEY DO FULL RESTORE, REcapping, etc etc. great lil place. Used them twice, both experiences were good.
I am reaching out to local places. What would the most likely thing to do for this amp? New caps...what else?
Thanks for that anecdote. You know, this thing isn't worth much, and I know it's "mid-fi" but it has this nice warmth and thrust that's hard to deny. I am not looking to pretend it's something it's not, but it would be cool if a small upgrade made it sound great.
I cannot say what it will do for the 535 but if my experience with a CJ preamp is indicator, it will be worth the $$$. Of course, you don['t want to spend too much. Nine was $200 for cleaning and checking and new  top of line Nichicon caps.

The 535 was a decent amp in its day and I remember many saying it was the best sounding of the 535,545 & 555. I suspect caps and cleaning will bring it close to new.