grr lets try this again... just typed a long reply and lost it all!! <sigh>
Anyhoo... I wouldn't be concerned about the closure of the place for 1 months cos of Parvo, personally speaking I see that as a very responsible thing to do rather than a reason to be wary of them. You should always be wary of gossip in rescue circles, very often other rescues bad mouth others in the same area, why, I have no idea, but they do.
I don't see that the donation amount has really any relevance to what you are or are not getting, our donations never cover what we pay out for any cat or kitten so that shouldn't be what its about at all in terms of'what you get'. In short they may just not be able to afford the vaccines!
I would clarify with them as to whether the worming they refer to is the routine 9 week worming and if they have done the routine worming at 3 and 6 weeks with Panacur or similar wormer. Re the treatment for fleas.. did they have fleas when they came in? were they treated when they came in? if so, I wouldn't be overly concerned about it, just have it done when you get them. You may also want to check if they have been health checked by the vet prior to homing.
Our policy is that we are open and honest, if someone asks us a question we'll answer it with the truth regardless of what that truth is. Not everywhere is the same but that said you should be able to ask questions about the running of the rescue and their homing policies, care of the cats etc without being made to feel you are prying.
If you have genuine concerns over something you have been told directly or saw then I would raise them with the rescue directly but do be wary of casting up 'gossip' as whether it is true or not, it may still offend.