and with the weak job market it seems I can only move sideways into another support role
This is not always a bad idea. Even if there was room for progression at your current employer, if you do not enjoy working the helpdesk there, then you would not enjoy any IT position at that company. Helpdesk can be OK, if there is someone else successfully working to improve the issues that you constantly get called for. If you have an IT job with no user contact at all, then you are truly useless.
One problem in IT is that users and managers think that an IT department's job is only to fix problems. The real problem begins when an IT department thinks the same thing! Another is that people always expect managers to define their job, and managers are always looking for people that define their job. After being in IT for almost 10 years, I now enjoy it (working for a small company helps). I didn't enjoy it for the first few years.
In my opinion, IT is satisfying when you do this (not a complete list):
1. Decide that helping users means developing relationships with them, and convincing them that you respect them (This is called "customer service")
2. Decide that you are solely responsible for the company's use/lack of technology/systems
3. Communicate to your manager what your job function is for
4. Learn how your managers view their own job function
5. Be proactive, find solutions/systems, and financially justify them on "paper"
6. Work somewhere where your manager understands 1 through 5
That said, if you can afford school and you enjoy it, then do that.