I know what you mean, Noddy. I totally go back and forth on that one. I have four main categories that I'd consider and I'm not sure which one to go with.
1.) Plain old party. Cake, some games. At home. Nothing too fancy.
Positives: Is anything else really necessary? Negatives: Sozlet and her friends have LOVED the rather labor-intensive at-home parties I've put on so far, and I just kinda like something about that. I think it's cool that Butrflynet's mom put that effort into her kids' parties, and that her kids have such fond remembrances of them.
2.) Party at home but with some extra oomph. Animal guy for 20-30 minutes, an extra-creative theme, that sort of thing.
Positives: Can be more creative and WOW but can keep costs down by having it at home. Negatives: More expensive in terms of time and money.
3.) Party at an outside venue that's pretty bare-bones.
Positives: Much easier to do in terms of preparation and running while it's happening and clean-up. Still some room for creativity in terms of the party-room part. Negatives: Seems kinda boring and conformist, and even if it's still bare-bones it's pricey.
4.) Super-cool but expensive party at an outside venue.
Positives: Just plonk down the money and forget about it. Negatives: Money!
I can't imagine spending more than $150, and that's a stretch itself.
One other thing I'm considering that doesn't really fit into any of the categories is that the circus is coming to town right around her birthday (Ringling Bros.) and tickets are as cheap as $8. Not quite sure how it would work, though. Circus theme stuff at home, then transport 'em all? Just gather there?
Right now what I most like is the idea of having an animal-theme party (zoo, safari, something) at home, with a person coming in with real animals for some but not all of it. So have your standard games (pin the tail on the kinkajou, what have you) organized around that idea, and then a brief highlight in the midst of an otherwise pretty normal party.