You didn't mention the 'wife' factor... That changes EVERYTHING!
But seriously I have a little dimension at home and the fan was running on it more than I'd like. I have 2 cats and the there was plenty of dust/fur inside of it blocking the air ways. Pulled a lot of the dust and hair out in layers and it seems to have helped, but I think the air ways got congested faster than they should've (less than a year).
It just depends on what you're willing to chance. The dimension may outlast the low-end server, it might not. If it your "home server" the dimension might work. For the small office server the poweredge would probably be more appropriate. Also take into consideration that the poweredge will be noisier if you are going to stick it next to your wife's desk.
Did that help or make it worse