Thanks for the feedback...
First off, thanks for some good ideas from Capellen,Fenes 2, and Kyramus. I probably won't use those exact suggestions, but I think y'all have sparked a few fresh ideas for me to polish up before next session.
WizarDru, I think you're dead on in your assesment. Dropping them in a crypt does sound fun....
JERandall, Jasperak, Paul_Klein, and jasper have all asked, basically, should the party even be in this situation. I thought about going into more background and motivation in the OP, but thought it was too long - so here's more stuff that will hopefully answer your concerns. Oh, and Paul_Klein, thanks - I've tried to make my world interesting for the guys; glad you thought it sounds interesting too.
Why are they in the ruins?
The party has done some work in the recent past for a sage/wizard/Elminster-type. The sage is trying to unravel the mystery of the reason(s) behind the WCE, the mechanism of the WCE, and whether the effects, (which are slowly fading) can be tinkered with to accelerate the fading process, thus 'bringing back' the gods faster. The party has been of some assistance in the past, and were asked to: investigate the Blackmarsh to confirm that the ruins existed at all, explore the ruins if located, and get into one of the towers if possible looking for clues (maps, diaries, spellbooks, histories, etc.) that would help the sage in his research.
On a personal level, one of the players is a cleric, and wants to help his deity in any way possible. Not to mention that he has to perform certain types of (holy/religious) tasks in order to be able to get higher level spells. The wizard is motivated by the possibility of finding 'lost' magic - such as may be found in an ancient city of magic. The psychic warrior is concerned with the return of the gods out of fear of (possible)religious persecution of his people.
Is this too high a level of challenge for the party?
Yes and no. I lifted most of this section of the adventure from a published module for 6th level characters. I've made a lot of storyline changes to the module to fit in my campaign and toned down the encounters to what I think a group of 3rd level guys should be able to handle, if they play their cards right. The operative word of course, is 'should'. The way the guys are taking their initial approach to the ruins is putting things in doubt, and the reason I started this thread.
What do I expect them to accomplish?
I expect for them to get into the tower eventually. It won't be easy, however, or done in one day. I expect the party to be lurking about, exploring the other parts of the ruins for several sessions, at least, before taking on the tower itself.
They have reason to believe that as long as they don't overtly attract attention to themselves, they can move around large parts of the ruins area without too much danger. Scouting and recon shouldn't be hard. They have reason to believe that some of the previously looted crypts have a lock similar (though presumably less powerful) to the one on the tower - maybe a dry run to test the plan would be smart? Well, yes it would, but I haven't heard anything about trying that route. They know what some of the caste markings look like, and what they mean. Have they thought about trying to alter their low-caste outfits to mimic someone of higher caste, thereby increasing their potential areas of exploration? Not that I've heard.
Anyway, hope the additional info answers your questions. Thanks again for the feedback.