I think mostly I don't do this (at least part 
I).  In fact, the last big wish item I lost out 
on (pretty much a tragedy of errors in the 
bidding process), caused me to feel like -not- 
going for other cels for a while, because they 
just couldn't compare (but then a different wish 
cel popped up and again my wallet was empty ^^).  
All in all, I try to be good and conserve money.  
It's easy to quickly run out of money unless you 
try to be as picky as possible.  I'm not perfect 
though.  I think I'm more likely to impulse buy 
after I've been 'good' though and have more money 
than I'm used to set aside for my hobbies ^^

Early on in collecting I used to regret impulse 
buys.  Some were cels I 'settled for' after 
searching and one or two were a little 
uninformed.  A few may have prevented me from 
being able to pick up something else I liked 
better.  Nowadays I guess my impulses are more 
picky than they were then, because I rarely 
regret them and they rarely prevent me from 
buying anything else (other than other impulses 
^^)  Sometimes I think I regret -not buying- 
several cels more...

Keys
...but the money for the cels I didn't buy, went 
to cels I love, so ^_^