A decision like this volves so many aspects of your life that it's difficult to offer any advice. My father is a college professor, and several of my close friends are full time tenured professors. Here are a few things I'd consider, however.
Employment prospects
Full time college teaching positions are very, very competitive to obtain. I'd say the market is even tighter than the legal market. My dad teaches at a non-prestigious state university. When positions open up, which is rarely, his department has the luxury of choosing from several hundred applicants. The people who get hired, even at his state commuter school, invariably have Ph.Ds from places like Columbia, Berkeley, etc., and are well published. One of my good friends got his Ph.D from UCLA and spent years teaching part time community college courses before landing a full time gig.
Like law school, your employability is tied to your pedigree, but it's worse. You can't be a solo practitioner college professor, and even small colleges can be very picky about hiring.
Do you like research and scholarly publications?
The Ph.D will not be enough. You'll need to publish like crazy in order to build up a reputation so that you can get hired. Many people like teaching but aren't thrilled with the peer review/publishing aspect.
Are you willing to live just about anywhere?
If so, you may have a better chance at employment. A small college in west Virginia will be less competitive than, say, NYU, but it will still be far more competitive than most people expect.
My views on Ph.D programs differ somewhat from my views on JD programs. Based on what I've seen, a Ph.D from a so-so university is probably not worth it. The field is simply too competitive.
The good news is that it's quite common to get substantial or full scholarships for a Ph.D. If they accept you, they'll probably offer you money.