How important is the amp?

The amp is pretty important, but a lot depends on your speakers. If the speakers are meant to be driven with transistors, its likely you will not hear a lot of difference between amps. But if the speakers are meant to be driven with tube amps, you may hear pretty dramatic differences. Some speakers can be driven by both, then you can compare what the differences are between tubes and transistors and again the differences can be pretty profound.

I would think that good conventional speakers should sound good with both transistor and tube and hybrid amp, just different. Electrostatic, horns etc may be another matter.

10-08-15: Inna
I would think that good conventional speakers should sound good with both transistor and tube and hybrid amp, just different.

Nah! I don't think so. I'm in agreement with Ralph here. if you look at the speaker impedance & phase plots you can tell whether the speaker was meant to be driven by s.s. or by tubes. Also, talking to the speaker manuf can reveal some important info such as what amps do they use when they "voice" their speaker. All this leads to the correct category of amplifier - tube or ss or hybrid, etc.
A speaker driven by the wrong sort of amp can sound terrible...

Mordante,
this is probably a biased view since I'm a big fan of Symphonic Line amps myself. I've had experience with the RG4 Mk3, RG1 & Kraft 300 amps. Symphonic Line amps are really very good & can drive most speakers. So, if it were me, I'd wait till the last minute to upgrade the La Musica amp.
having Said that a friend's friend got the Kraftwerk & found it to be a superb amp. I don't have knowledge of how the La Musica & Kraftwerk amps compare.

If you like what you hear and can hear differences when you tweak then I can't think of a good reason to change.

Wait, oh yeah, because there is always something better!!! of course! You never know for sure sometimes unless you try.

If you are content, you will just enjoy listening to the music. If you are not, don't loose sleep. Look for something better now! Money and time is all you have to loose.

Seriously, only you know if you are happy with what you have, but in your case, it sounds like the vital signs are good.