If I spend all my time improving myself, it comes at a cost.
This is a really interesting thought and I'd like to dig more into it.
How does 'self-improvement' actually happen?
Theoretically, being mindful should help with self-improvement. By being aware of what's happening right now, people should be able to notice things that would've passed unnoticed otherwise. Furthermore, by noticing things, people should also be able to improve the noticed aspects of their lives - or the things they're doing - that don't feel right.
If you were fully focused while reading the previous paragraph, you should have noticed that I said 'people should' as opposed to 'people will'. The reason I did that is that, somehow, people always feel that self-improvement comes with future plans and that the present is unfortunately already gone, which means there's no way to improve anything there. Therefore, being fully aware of what's happening won't help with making what will happen next any better.