Are you aware of the house rulesregarding chargen? Just in case. Still sleepy.
IIRC, there's no list of side effects, but we can try to find one. What you describe sounds a little too powerful for me, because it'd imply that casting any lvl 05 could double as a suitable InVi spell of, say, lvl 25 (base 4, +1 diam, + 4 vision). I'd say drop that to "identify nature of vis by touch for diameter" (lvl 10), which means you must know or suspect something contains vis.
Based on the only exemple we have, I might try to suggest creating your side effect as a temporary minor virtue, with a possible drawback. Like, casting a spell gives you 1 more confidence score (not point) for a Diameter, but sometimes makes you feel a little too confident. Hard to judge, anyway :-/
Lesser/Personnal Powers: look at creatures for exemples. There are some on the wiki (familiars, ghosts, beasties) that may inspire you. Look out for spells, too. Any spell of level under 25 can be built as a Power.
A personnal power giving you Vis sight is perfectly possible, although it'd cost fatigue.
A lesser Power changing a Gem into any other would be possible... But it wouldn't last (Muto) 
You could take one to make gems more malleable, but, since you're a verditius, this is useless (you've got a build-in ability for this). You may have a Personnal power to sniff out gems (serf's parma).
Taking a power that correspond to a Te/Fo combo you're weak in, or maybe defficient, might be a good choice. Dunno.
I want to sleep.