guitarman,
Welcome home!
We have alot in common already, I'm primarily a guitarist that uses an arranger for my back up band. BTW I have a maple blonde ES 175, as well as other assorteds.

So as for my take on your Q's:

For keyboardists, are these different instruments like say the difference between a Fender and a Les Paul for the guitarist?

That's a pretty fair assessment. Most of what all of us are using is high end so it's a matter of preferences both in sounds and interface. One board is a bit mellower and the other a bit more straight ahead....depending on the listener of course.

Not as much of a difference in solid vs hollow perhaps more hollow to hollow solid to solid.....Martin, to Gibson or Taylor, etc.

The one thing about the vocal inputs on the boards, is the vocal harmonizer that can be very cool to use.

I do not use the line inputs for the guitar, as I see no need to with my setup.

As far as the fervor over different new boards...I'm still very excited about getting my Tyros. But we have discussed it quite a bit already as the new kid on the block and I think now there is just alot of wait and see when some of us in the states get them. As well as there are other good boards we have been discussing as well...Ketron Genesys etc.

About the built in speakers on any of them IMO opinion in a crowd of 30/50 drunks.....if you want to be heard, I would count on getting an external amp of some sort.
again welcome and jam on,
Terry