there are a handful of rather enthusiastic front paging monks

I suppose I must be included in this category. Yes, I freely admit to front-paging lots of stuff these days. Just about anything that is well-written, interesting, not answered, answered well, FAQish with a twist, obscure, funny or otherwise strikes my fancy is meat for the grinder.

The main reasons is to reduce the time that nodes stay on the front page, thus reducing the impact of reputation inflation. The faster a node moves off the front page, the lesser the effect.

And as an added bonus, an irregular reader who visits will see a fresh page each time. And that is a Good Thing.

And then there is the case of CUFP. I used to watch CUFPs stay on the front page for months. These days I front page nearly every CUFP posted, because Cool Uses For Perl are by definition worth showing off.

I don't see why you think 50% is excessive. The question I ask myself is more along of the lines of "is this node and each and all of its answers so poor that it does not belong on the front page?" And I find that by and large I usually find that the answer is No.