For a flat-file database that's available online to a limited number of people, a spreadsheet is perfectly adequate. It's probably heresy, but Google docs would work.
Yes, I'm sure that's the right kind of solution for on the day and most of the potential use cases.
I'd imagine that all of the data gathered would be within scope for Wikidata, though I'm not sure whether Wikidata yet has good structures to record constituency-level election data. It would be great if it did.
Chris