Is it worth to update to an x64 environment?
Well, memory management will be much better in a 64bit platform.  This is because all the memory is real memory and there's no concept of extended memory any more.

This means that you can now have much more than 1 Gig of execution plans in memory at any one time.  If you've got lots of stored procedures you are probably generating new plans for queries all the time because you can't store all the plans in memory.

Granted this ability to grow the plan cache beyond 1 Gig will take away from the buffer pool, so that's something to keep in mind (no you can't control how big the plan cache is).

Joins of 4-5 tables with 100k records each isn't all that scary.  When you get into the 100M range that's when things start to get more interesting.