Actually, the sim_mem_access_xxx() functions trace addresses not data. The only way to trace data is to redefine the LDW, LDH, LDB, STW, STH, STB, etc. macros as a filter. There should be an example in the distribution on how to redefine a filter, and if I recall correctly someone else posted some examples in a previous thread. You may have to play around with the 'as' script to insert your own filtering scheme, but it shouldn't be too hard.
If you have success and want to post a generic mechanism to trace instructions, I'm sure others will appreciate.
-- Paolo