Lots of conferences have (IMO) very heavy registration fees, but along with pay-to-publish journals, this does not seem to deter people (presumably because the fees are taken from a research budget). Organisers who accept every abstract though would be hard to prove. My interest (sadly) is academic / scientific posters & poster events remain a popular conference staple. One of the issues people raise though with posters, is that it is a 'lesser publication' as organisers seem to have huge rate of acceptance (if accepted, you will pay their registration fee). I don't know what firm evidence their is of this and if the angle is to view the 'robustness' of the presented material (although how this can be gauged solely from an abstract of 300 words I don't know), then I can understand this approach. If the angle is to produce a focal point around which to network however, then a hall full of people with basically A1 signs which say 'If you are interested in ..., then stop for a quick chat & see where it goes', may not be such a bad thing.
For me, huge fees are a no-no as I view money as money, be it my own or somebody else's which has been allocated to my budget. Meet loads of people who are willing to talk about some aspect related to a theme you are interested in - yep. Listen to someone who expects academic recognition solely because they have 'published' in conference proceedings (different if you have been selected to give a scheduled oral presentation) , .... I'm still out on that one ;-)