Amp vs Preamp which is more important?

If you have not already Tube Rolled the Input Stage on the Pre-Amp and Power Amp, there is a trick being missed.

A Investigation on Tube Options and trials may just deliver what is being sought.

I would make the best Tubes available for the Pre' as the better the signal is processed at this the device is for the benefit of the Power Amp.

Trying different Umbilical's at all interfaces can be tried out, these being selected for their allowing New Tube selection to really show of their magic, will be a very cost effective way forward.

I can't say enough good things about PC Triple C wire used to produce Umbilical's and Speaker Wire. 

Holy moly,

They are both important.  But consider this: If the preamplifier omits anything (no matter how subtle), it is lost and can never be recaptured.  This is only the tip of the iceberg so to speak. Now extend this singular example to all the miniscule details that must happen correctly before the amplifier ever gets the signal.

The amplifier has to be faithful to this small input signal and produce/amplify exactly what it has been given. All of it's attributes must be in keeping with the loudspeakers.  This is synergy and without it, the reproduction just won't work. 

Addendum,

A truly great preamplifier will not be system dependant. Amplifiers must be considered with the loudspeakers that you will be using. Very efficient speakers may match up well with SET amps, etc. Less efficient speakers will require a more powerful amplifier.  Purchasing decisions must be in context with loudspeaker consideration (s).

BOL

Seems the preamp is what needs to be updated in the OPs chain as it’s a weaker link than the amp.

Ah, the old 'chicken-or-the-egg' conundrum.....as noted in several of the posts above, 'synergy' is the key-word here. The trick is finding what amp best mates with the preamp.....while many solid-state amps can have slightly different colorations, the preamp affects the overall end result more than the amp. Of course, the caveat is that the speaker is the biggest wild card in the deck, so that should be the first component chosen (IMO). I feel that most of the time,'bad' sound is a result of a poor recording, not the equipment's fault. Mass-market budget gear from places like Best Buy and that ilk is the obvious exception. Anyway, one of the most fun parts of our hobby/obsession is swapping components and cables in the never-ending search for the Holy Grail. YMMV.