All depends on how it was driven and if it was tuned correctly for the mods. Most people end up modding their WRXs and its never a problem, especially at basic Stage 2, which is what the 06 is currently at.
However, can you be certain it was tuned? A BOV is generally an unnecessary mod as well, especially if it is a vent-to-air. Plus, do you know how/what it was lowered with? Sounds to me like the 06 could just be a headache waiting to happen if you don't know anything about it. I'd pass.
Considering looking for a 2009 over the 2008 since they had a very nice bump in power that year.