My thoughts on the new backglass is that some people with blown out back glasses wait til they go to sell the machine and then feel they need to replace it in order to justify the cost they want to get out of it ($800-900 or more). So, the new owner gets all the enjoyment that you could have had for a few years anyway. Now, if you plan to sell someday with current crappy backglass, then no worries of course.
Having said that, I could probably use new backglass myself (though current one isn't that bad) and just can't seem to pull the trigger... so that's my hypocritical post for the day!! LOL. But if new playfields ever get released, you can bet I'm buying new PF and new BG immediately and making this a top tier game in my collection.