1.Sweeping without a pick is like tapping With a pick-very cheesy-no matter how many exceptions there may be.
2.Should you learn sweeps-well does a plumber come to your house with just a pipe wrench ? Or your cable guy with just a pair of pliers ? No. Every guitarist is only as good as their "toolbox".Context and using the right tool for the job are pivotal.Sweeps are just another tool.So yes,if for no other reason than diversification of knowledge and style you should learn sweeps,and a plethora of other techniques,and USE A PICK!!!!(at least medium gauge)
3.The longer you extend your arpeggios,the more fretboard coverage you achieve,the more flavor and originality you bring to a sweep,the better.
4.Almost every contemporary "relevant" guitarist of note use arpeggios in some fashion.Be it tapping,triad sequencing,or full-on 6 string extensions.Remember all music is comprised of scales and chords,an arpeggio is simply a chord whose notes are played individually,as opposed to in unison(harmony).I can't imagine even debating this issue.Sweeps are an essential part of a guitarists repetoire,no different than tapping,speed picking or phrasing.
5.Exercises are fun and useful in practice.However,listening to sweeps "in-action" in the context of a song are often the most instructive.For really great sweepers I suggest listening to Richie Kotzen,Tony MacAlpine,Jason Becker (Perpetual Burn),and of course Yngwie Malmsteen.I'm sure there are others I have accidentally omitted.