I wouldn't mind a series about Cadets if done well (though it does have the potential pitfall of just becoming "future teen drama"). It would have a set run of four years, could focus on a core group of say six characters (maximum of two full-blooded humans), with potential for plenty of recurring characters as well and the occassional cameo from other series (depending on when its set).
Setting it on Earth for a year might not be such a bad thing, as it would force TPTB away from lazy stories that involve space anomaly / alien of the week, which winds up with lots of complicated technobabble or phasers firing. They would have to focus of characterisation, development and relationships between the group, looking at the future of Starfleet before they know what they're doing. It would also be (to a large extent) serialised, with previous events impacting on their lives as they work towards the ultimate goal of becoming officers, which would avoid the damn reset button VOY favoured.
The characters would also move away from their set duties, as you wouldn't necessarily need someone who is an engineer, doctor, etc. There would also be one who saw themselves as the 'leader' and others who would know what they wanted to do with themselves, but then you'd also have the aimless ones, who were brainwashed by recruitment adverts to enroll. Plus there would be no reason for inappropriate low-cut, skin-tight catsuits, as they'd all be in uniform.
Then when they get out into space then it could become more of an anthology series, with all/most of the characters gone in different directions, what they get up to and experience, as well as having potential of building up some big plots that bring them all back together.