I think that would be wise. The 694 is an underachieving chipset, and the lack of memory throughput can only cripple you more as you have two cpu's to feed with data. I would either think about a BP6 Abit (440BX) or the AMD route you mentioned. I assume BP6's can be made to work with P4-S's, but you might want to spend some time in the SMP section of the forum and get a better feel for what the viable and cost effective solutions look like.
I don't think I have to tell you I'm not a big SMP fan, only certain tasks really respond to it. Be sure you are realistic about what your uses for the machine include and how responsive those tasks are to SMP. It may be better to put the money into something like a HT P4, or perhaps just an evil fast Tbred B or non HT P4 rig.