If you don't regard your lawn as a feature of your garden and you only use it for recreational purposes, then cutting and producing a mulch wouldn't be a problem. If, however, you want a pristine, healthy lawn, then I would collect the clippings for compost. As regards a scarifier, whatever method you decide would be worthwhile as it would clear the build up of mulch or dead grass thatch as grass grows from its base.

Scarifying once a year would do nothing but good if you are looking for a show lawn - you would be totally astonished by what you collect! A scarifier will collect lots of moss (if you have a moss problem) as well as thatch from lawn mowings etc. Our mower collects the clippings but scarifying still produces a lot of detritus. I would quail at doing it on an acre...