Elsewhere, Adcom amps of that series have been said to be better the lower the power, as long as your speakers are getting the juice they need. In other words, as you get more watts you pay for them in sound quality. So it is possible that you would notice a difference if you moved from the 535 to the 545 or the 555, but you might not like it.
Aball's experience would seem to confirm the idea that lower-powered amps in this series sound better. Of course, he is planning to sell a 545... ;o)
My best 2 cents is that Warnerwh and Chiho have very good advice. Upgrades are expensive--less if you are doing it on the 'gon, perhaps, but chancier too, since here you can't listen before you buy. It makes sense to take the biggest possible step each time.
One good SS amp I have owned is the Sima Celeste W-4070SE, a nominal 70-watter that sounds like a lot more. Bigger models in the same series were the W-4150SE and W-4250SE. Simaudio no longer makes them but you can find info on their site, at this address:
(Sorry this is not clickable--I tried but the edit post page won't do it.)
These amps obey the Adcom rule--as they get bigger, they get just a little less lively--but any of them would be a real upgrade for you.
Then there are tubes, of course...