JMHO, but... Chasing the usefulness of that 32 ohm speaker by buying another one is a waste of money. You could probably get a well known and respected, proper guitar amp speaker for the same price. That is, unless you've heard this 32 ohm speaker and like it's tone above all others. The SS amp DOES need to be designed with the intended ohmage in mind IF you want to get the full wattage out of it. If you run the SS amp into too low a load it may over dissapate. If you run it into too high a load it won't deliver the intended power. The cabinet size is somewhat pedantic WRT guitar amps. Accidental resonances and peaks are part of why certain cabinets sound good with certain amps. Remember that a guitar amp is intentionally coloring the sound. And absolutely NOT trying to reproduce it accurately. That said... There are cabinet designs for roughly 30 watts that are known to sound a certain way for guitar tone. A VOX AC30 with a pair of Celestion Blues (or cheaper, but not considered as good, a pair of V30's) comes to mind. There are also many 1x12 cabinet designs that are very popular and should work well for amps from 20W to 50W.
Point is... If your going to spend money on a speaker for guitar, buy a guitar speaker. Don't try to make the 32 ohm speaker useful by correcting it's load with another 32 ohm speaker (unless you like that speaker, as noted).
Another note... If your feeding signal from the "host" amp to the supporting amp properly, the tube amp should be oblivious to the needs of the SS amp. So the SS amp and it's speaker load is the only formula you need to consider.