Is It Worh Modding An Amp

I'll also say No.

I’ve sent two pieces of gear out to be modded and wasn’t especially pleased each time.

The first was an Adcom GFA-555. It was away so long, I honestly couldn’t tell if there was any improvement. But I was out the money.

The second was a TacT 2.2X. The modifier fell on hard times and never finished my job. Indeed, I never even got the unit back -- a decade ago, it was in pieces somewhere in a storage unit. That was a total loss. Not the usual outcome, but it can happen.

In any case, modding is a poor financial move. Modified gear costs the owner more but is more difficult to sell (and usually sells for less) than unmodified gear.

You could roll the tubes.

Most tube upgrading services involve swapping out parts, primarily capacitors, for more expensive ones.  This is not necessarily an improvement if the original designer voiced the component and used appropriate parts for the sound the designer was trying to achieve.  I've heard several such "upgrades" that sounded clearly inferior (at least in my opinion based on my taste and the system the amp was tried). 

To do this sort of thing correctly, one must find a technician who knows about the sound of different parts and you must convey what you want from the upgrade (e.g., warmer/lusher sound or greater clarity, etc.).  There is no such thing as an always superior part.

Your best bet might be something non-invasive such as the tube rolling suggested above.  Manufacturers put it the cheapest and most plentiful tubes that will fit their needs.  They need tubes that can be easily replaced so that they can either supply the customer with replacements or make it easy and economical for the customer to replace.  That is not just a matter of saving money.  It does not make sense for a manufacturer to invest in expensive tubes of a particular type when that tube might not fit the customers' taste or match the customers' system.  It makes more sense for the customer to do this.  

Even though I'm a tinkerer by nature, unless there are some known issues with the amp and some known mods to fix the issue, I would not modify the circuit.  Tube rolling is a far safer bet.

On the other hand, has anyone done any cap upgrades to these amps?  I don't see that as a circuit mod, just a parts swap....and it's reversible.  

There is a thing you could 'mode' and it should upgrade its sound without the doubt. Prima Luna, as well as many other manufacturers in such and even in higher class use Alps volume control. It is in fact the crucial and weak link of many preamps or integrated amps. By changing it, for some attenuator (Ladder type), let say from TKD, you will hear significant improvement that no tube or cable swapping can match, for a insignificant cost. Just be sure to buy the part that has the same values as the one inside and buy it from reliable source (not from Ebay and not from HK or China, as they are mostly fake, meaning not originals produced in Japan. Of course, it does not have to be TKD, but their TKD 2CP2500MC is a great value, performance/price vise. Its not expensive and you can always put back the original part back. Its not a difficult thing to do, for any experienced tehnician.