"I find myself drawing a blank about what I'd blog about, though. Who would I write for? What would be their purpose in reading?"
I hate to self-promote like this, but seeing as how I run a startup (in profile) dedicated to helping bloggers find stuff to write about and "cure writer's block" (our little slogan), I figure I should say something.
Yes, you should definitely, definitely start a blog. If you're comfortable with it, I'd say get firstnamelastname.com. I got paulstamatiou.com four years ago and have been writing on it consistently since then and I kept it professional and devoid of too many personal things. I talked about stuff that interested me (technology) and often lots of little guides showing how I was able to do this or that. A lot of my posts have just been about things I've been working with over the last few days. New piece of software that I find really handy.. blog post, but I try to add info that others wouldnt have.. tips on how to use that, or getting it setup quickly etc.
Over the years my subscriber numbers slowly went up and now I have a decent following. It's still more or less "professional" in terms of the content I put up there and it has ended up being a portfolio of sorts for myself. Was it worth it? DEFINITELY. It got me a Yahoo internship in California (and several other job offers), I've been flown around to check out various events for different companies, got invited to speak at a conference in Europe (and expenses paid), and I was even in a Nike commercial as they found me online as a "real" user of Nike Plus. Again, I dont want to make this like I'm tooting my own horn... just trying to say that you need to start a blog!
only reason why you might not want to start a blog:
*you dont think you would be able to write consistently
The only thing worse than not having a blog IMO is having one that hasn't been updated in weeks or months.
I could go on and on but I'll just point you to my HN profile where you can email me. :-)