I've done a few sportives, and usually enjoyed the experience. They've taken me places and I've met people I'd never have found on my own.
The availablity of a feedstop and a broom wagon add to the sense of security, and in most cases I think it's been money well spent.
Having said that...we looked at doing the local tour of the pennines sportive tomorrow with the wife. She's only just started road riding so we would be looking at the 60km route. Entry fee is £25 each..... sorry but not going to happen, £10 or £15 quid would be expensive but might have tempted us, £50 is just silly to ride on roads I ride every other weekend.
We will still go out and ride, may even weave our way across some of the sportive route, but the £50 will go somewhere else.