As a dealer I can safely say that if sold as a complete collection, you might get a small profit if taken as a whole but that would have to include the genuinely scarce pieces like the Kew Gardens 50p. The vast majority will go at face value if collected from circulation. I bought a complete collection of issued decimals in 2013 and still have most of the circulation pieces. Collecting them from circulation was no mean feat, but when everyone else can do the same, it eliminates much of a premium. Plus everyone wants coins with no marks if possible. One offs in sets sell for a premium, but not that many collect 1p, 2p, 5p 10p and 20ps, so you are left with profits coming from 50p, £1 and £2 coins. Nobody wants the £5 coins. If modern, most people buy year sets and get the job done in one go.