Frankly, I became a site sponsor because I thought it was still being run by an individual. Wasn't aware it was part of motorcycle.com. I generally don't like "contributing" to for profit businesses so I probably wouldn't have in the first place but since the restriction exists to only have 10 PM's in your inbox at any given time, It's worth my donation for the extra space alone. I like to communicate with people and keep those conversations for further reference so when it comes time to re-up, I'll probably do so for that reason alone.
Just so you are aware, there is an option to download your private messages. It's below all the messages in your inbox and it looks like this:
Download all Private Messages as:
XML | CSV | Text