We spend plenty.
Teams are limited by the NCAA to nine assistant coaches. Alabama has a bunch of non-coach coaches (often called "analysts"). So do we. That's what Hudson was before he became DC, for instance.
We don't know exactly what Kelly makes because Notre Dame - as a nonprofit private school - doesn't have to report it until its tax returns become public record. There's a couple-of-year lag on that. It's also hard to know what a coach earns that doesn't come direct from the university (apparel contracts, etc.). But it's generally believed Kelly makes $4 to $5M, all in. That's certainly competitive.
Assistant coach salaries are sometimes an issue, but BVG was being paid north of $1M, which would put him in the top tier of DCs.
There's always someone with a newer, fancier practice facility or whatever. But ours isn't bad. Same goes for the Gug.
I think you could have argued ten years ago that lack of investment in football was a problem. I really don't think that's the case these days.