I’ve written up a pretty thorough how-to guide for getting your hands in tip-top shape. You can check it out here.
It definitely does get quite thick after use, so the best solution is to buy yourself some nail polish thinner (NOT remover), and add that to the bottle. Keep adding it until it reaches its old consistency. You will have to do this more as your bottle gets low, but it’s cheaper than throwing away half the bottle every time it gets thick. They make a special thinner just for Seche Vite, called Restore (also by Seche Vite). I liked the way that made the top coat work, but it doesn’t last long unfortunately.
I’ve used only one other quick-dry topcoat besides Seche Vite, and it’s by China Glaze. It’s called Fast-Forward Top Coat. It doesn’t dry as quickly as Seche Vite, and doesn’t seem to work as well with thicker coats. It does smell better though. Haha!