So it seems would cost you $550 to own a refurbished EX442, vs. $250 for a refurbished St-140. You like the B&K sound with your speakers. You seem to have the $300 in your audio budget. The EX442 may, and possibly be likely, to prove better in your system. As aberyclark mentions the extra power will not hurt and might prove beneficial should you purchase different speakers. It seems that the only debate you have is the possibility that the $300 might be better spent on upgrades else where in your system. That debate could well be left for later. The ST-140 could be sold to recover some of the cost.
As, based on your original post, I am inclined to believe you WANT the EX442, go for it.
As, based on your original post, I am inclined to believe you WANT the EX442, go for it.