OP, I don't think you sound bridezilla like at all so Ignore comments like that.
Just Re-reading your OP and it seems like that originally it sounded like staying for 2 nights was the only option, and even if you did find cheaper accommodation I could see how some of them would be thinking they'd rather not do that.
if you have now suggested to them that they can just come to the evening do if they prefer (sounds lovely) at minimal expense to them,and they STILL make excuses, then you've done all you can.
People who genuinely want to come will come. Either to all of it or just some of it, both f which you're ok with which is good. The main thing is that you have now given people choices for their convenience. That's the end of your duty to be a good host as far as the planning of the day goes. Really, you have been accommodating enough. You could bend over backwards trying to do the right thing and you'd STILL get it wrong in some people's eyes.
In my view the most important thing is that you have the type of wedding YOU want, not what other people want. Yes, take people's needs into consideration but don't go overboard.
You have done enough. They either come or they don't. Stick to your guns about the spa day. It's YOUR hen do.
Can't think what more you can do now really other than just forget about any more excuses that come out of the woodwork, and look forward to celebrating with the people that DO want to make the effort to help you celebrate the day how you want it to be celebrated.
These people may not even be in your circle of friends in 10 years time - imagine altering arrangements to try and please them and not enjoying your wedding as much, and they aren't even in your life in a few years - you'd always resent how you changed your plans for them.