If there was a collision, the collider could spend any money sent to that address. Just money sent to that address, not the whole wallet.
If you were to intentionally try to make a collision, it would currently take 2^126 times longer to generate a colliding bitcoin address than to generate a block. You could have got a lot more money by generating blocks.
The random seed is very thorough. On Windows, it uses all the performance monitor data that measures every bit of disk performance, network card metrics, cpu time, paging etc. since your computer started. Linux has a built-in entropy collector. Adding to that, every time you move your mouse inside the Bitcoin window you're generating entropy, and entropy is captured from the timing of disk ops.