Better amp or better tubes?

With this lockdown I'm finding myself and I'm sure many others listening to music more often and with that my mind has gone into upgrade mode.
My amp is a rare Quickilver 300B that must be at least 25 years old using genalax gold lion  300b tubes.
Over a year ago I sent an email to Mike sanders asking him about suggesting upgrades to the unit and surprisingly he told me if the amp is working fine to just leave it alone. We ok then.
The genalax 300b are modest in price  costing about $300 a pair and have worked flawlessly. If I were to upgrade the tubes, what direction would you suggest? To be honest, I'm a bit apprehensive in spending a lot for tubes since they can fail at anytime. Am I being overly concerned?

So, do I upgrade the tubes or amp? Amp budget of under 4k.

Thanks