Should I replace capacitors in an old but working amp?


I have an Ensemble Tiger B50 amp which I purchased new back in the early 90s.   I love the way it sounds and really just want to keep it for as long as possible.   I leave it on at all times.
My question is should I just keep on keeping on or should I be replacing the capacitors after all these years.   I hate to mess with it as it sounds really good to me but I don't want it to burn up  either.

Thanks,
Steve
stephenss
Just replace the electrolytic power supply caps first after 20 years.

Film, mica, and non electrolytic capacitors can last for “almost forever”and I would not replace them.

If the equipment sounds like new, it is not time to do any repairs.

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The value of any electrical component can sway over time. Focus on resistor upgrades as well. If chokes and transformers have values written on them then have them checked too.

The tonality may change in varying levels for every item that you swap. Try changing out resistors and caps of similar composition to retain as much of the amp's current tonality as possible. I know from experience.  

If you recap do it in parts.
Section done, be very carefull if you replaced them correctly sometimes the cap you took out is in incorrect plus or minus on the pcb printing. Get one out place the new one back in exactly like the old electrolyte. Ignore if the pcb board printing is otherwise. 
Most of the time pcb boards where ready for production, but later on they made mistakes. Then they put in the electrolyte the right way but the drawing on the board was wrong.
OK I would go for example 100uF 25v to 105 degree types nichicon but the 100uF 63v types. The higher voltage the electrolyte can handle the lower the esr. 
Or place two 47uF/ 63v parallel even better. Lot of small value microfahrad to combine the original value ( decoupling)
Most of the time the coupling caps are still good, but when your in recapping I would replace them too, look for high performance types mkp.
So clean all contacts look for bad solder joints they will give noise later on. 
Clean potmeters clean every soldier joint even the existing ones, doll looking joint most of the times they are bad in sound quality it pays of to clean it very well.remove Flux with 96% alcohol.
Board for board check every board if your amp is still working well. Better to find the fluke now then to search in AL your done boards. 
Goodluck take your time don't rush
Replacing the electrolytic caps with film caps if they can fit in the space.