Bandwidth usage I'm sure hasn't changed (and is actually probably lower, I'm sure most of us aren't spending nearly as much time on here recently). What seems to be taking a lot of time is certain database queries and inserts. If you're geeky enough to know which pages likely require the most database work, you'll see the slowest parts of the site tend to be those areas, while pages that require less database access are much faster. It's near impossible to say without access to the server, but it appears to strictly be a database issue.
It makes me wonder if there's a bad index in one or some of the tables, or some other data problem in the database. It seems far too slow, especially during the middle of the night when the servers are probably very lightly loaded, to be strictly a problem with the server being overloaded. It took literally over 3 minutes (my FasterFox extension times page loads, so that's exact) after I hit "Submit" for my post to show up yesterday at 1:00 AM Eastern time.
But I trust those who run the place know exactly what's going on, so I'm going to shut up now.

If you guys would like another opinion from a guy that runs a significant hosting environment, feel free to email me. I don't want to sound like a back seat driver.
I'm another that thinks a paypal donation button to help with hosting costs is a good idea. Also Google AdSense is at least worth considering. A similarly sized forum I run makes $300+ a month off AdSense.
I don't think making it pay-only is a good idea for the same reasons some others mentioned.