The question, if the Greens were going to make more gains, is "where?"
Two of their possibilities are Bristol West and Norwich South, both currently LD held with large student bodies. But Bristol W is held by a very popular Liberal incumbent with a staggeringly large majority and a strong Labour challenge to compete with, and Norwich South we have a poll from that shows Labour absolutely streets ahead, having narrowly missed out to the Lib Dems last time and taking a large chunk of their vote now. In Cambridge, the only other LD held Green target, the Greens have fallen back locally since 2010 at Labour's expense. So if I've underestimated the Greens, I don't think it was at the Liberals' expense in terms of seats; certainly the LDs will lose a lot of votes to the Greens, but in most Lib Dem seats either the LDs are too entrenched and the Greens are just tussling to take off disaffected votes that would otherwise help mount a Labour challenge, or Labour have managed to anchor themselves as challengers, or most importantly in many cases they're not actually studenty seats at all.
Students will swing to the Greens, I don't doubt, but with FPTP that won't be enough to gain them seats unless they can take a lot of local city votes as well as galvanising students. Students have notoriously low turnout and the Greens just haven't got the publicity, voter base, and traction to take the city voters they need in sufficient quantities in any one seat, most of whom they need to take from Labour.
Norwich N is certainly a Con/Lab marginal - well worth voting Labour if you want to remove the Tory. The city areas are solid Labour and form a lot of the less university-based and some of the less well heeled bits of Norwich, but the seat also spreads out into some rural wards that are rock solid Tory. UKIP might make a small dent but it'd be an equal dent in both sides, and there's none of the more leafy, educated, or touristy areas that tend to be naturally more liberal.