I haven't seen much mention of Sudden Widen, but I think that is one of the better sudden feats. With AoE spells, the +100% effect doubles the radius of the burst causing it to cover a much larger area. Whether a larger blast zone helps much will depend somewhat on the situations faced and is thus campaign specific. In many of the encounters in my campaigns, a Widened spell would often allow it to hit anywhere from 1.5x to 2x the usual number of targets, perhaps even more in certain spots. Having that ability just 1/day would be very handy.
For lower level casters, Sudden Enlarge applied primarily to certain short range spells (i.e. Scorching Ray) can be quite helpful. However, at higher levels, the range issue is generally less of a problem, both because those spells reach further, and the caster usually has enough other spell options with larger ranges.