I'd think any maintainer might be somewhat leery of someone coming out of the blue asking to help with the maintenance of one of their modules. There's also the problem that if you just pick something at random now you might get bored with it n months down the road and then the module's back unloved again.

A better route might be to just do your work and find out what modules you are using regularly and then work on improving those (fix bugs, submit patches, etc). You'll be more likely to keep involved since it's your itch that you're helping to scratch.