I've used this kind of residue from precooking meat in three different ways before. A tablespoon or two added to a curry lifts the flavour a lot, but go easy because adding too much will cause the flavour to dominate the curry too much.
Second use is to shortcut while precooking the next batch of meat. Just adding the stock residue from the first cook will introduce all those spicy flavours without needing to mess with frying new spices, onions, tomatoes, etc. It's a big time saver that way.
Final use is to freeze it into sticks in baby food mounds and add a couple of sticks to cooked pasta as a fast-food easy dinner for nights you get home late and want something quick and easy to cook.
Definitely worth keeping and not throwing away. I wouldn't however suggest adding to base, this is just going to make a strong flavoured base so all your curries taste the same.