I think you've got to look at this as two completely unrelated decisions and make your choice based on what you want out of the hobby. As RM-MN points out you can start doing all grain now with minimal investment so it doesn't have to be a cost issue where you can only do one.
I started kegging very early on because I detest bottling. It's not difficult but for some reason I just hate pretty much everything about it. I know some find this ridiculous, and I've even heard some say they find bottling relaxing, but like gnef I don't think I would brew nearly as much if I had to bottle every batch. As someone also mentioned it's great to be able to pour any quantity you want without having to drink or waste a whole bottle.
The decision to brew mostly all grain for me is largely about control and variety. There are so many things you just can't do with extract - like the wide range of malts that don't come in extract form or the ability to control fermentability with mash manipulation. I love tinkering with recipes and ingredients and IMO the best way to do that is with all grain.
Good luck with whatever you decide.