A study by the US auto insurance industry came out last month - 38% less fatalities on bikes with ABS. If you think reducing your chance of dying on a motorcycle by 38% is worth $600, go for it. Studies can mislead, but even with some other factors assumed (type of bike, type of rider with ABS), that is compelling. It's compelling enough that I've been thinking a bit on how I can swap out my otherwise perfectly fine FZ6 for something with ABS. This percentage is similar to fatality reduction wearing helmets (50%?). Most of us wouldn't dream of riding without a helmet. Why don't we think like that on ABS?
Additionally, we had a thread yesterday on people who have done low-speed crashes in parking lots when someone pulled in front of them. They grabbed too much brake and locked the front wheel and went down. I've experienced that myself while practicing quick stops. I locked the front wheel a bit and the bike was totally unstable (but I caught it before going down). It's not an issue of over-rotating a stoppie and flipping. It's an issue of grabbing too much front brake too quickly, locking it, and going down.
I'm starting to develop the opinion that for the risks we take by riding a motorcycle, we should all embrace ABS to minimize some issues. I only wish I was at your point now - simply deciding to spend $600 more on ABS. My decision point is to sell the entire bike and start all over. Way more expensive. Even if it would cost me $2000 - $3000, it would still probably be worth it for that extra safety. Unfortunately, spending that money isn't in the cards now.