There is always extra utopium either in the trees, the utopium mine and in the sheriffs credits there is always one person with a utopium on his card. Also from the surprises.
Check the town hall when a question mark appears above it, you'll get a hint.
Characters you can't splice at the moment will be grey in the splicing menu.
Watch out for hearts appearing above your dwellings. You can use these to get extra rewards.