The best investement that one can ever make in startup is brining the best people on board from the very beginning. The beginning part is very important here. Times when the company is small and nothing is done yet are very critical and shaping. You can hire a bunch of fresh graduates that know nothing about software development later and you will be ok. It might even be necessary later on, as it is hard to get a superstar singer to sing on your bar mizvah. But, hire incompetent, or just not good enough people as the core of your startup and you are doomed.
The core people lay a foundation of the future products. Decisions they make are like a planted seeds. If they are good, you will get a healthy oak. If they are bad, all you will get is a small bush. The beginning phase is very decision intensive: what version control to use, development platform, coding conventions, how formal development process should be, what documents to write and how, product architecture definitions, specs, future growth and vision. While not curved in stone, these decisions are very hard to change later if not impossible.
In addition your core team will set high standards for the other company members. Once you get into company with good programmers, your natural tendency is to get to their level and stay there. Unexperienced programmers learn a lot from core guys. Core people feel themselves as mentors and do they feel good about it. The company starts with a high entry level and continues to climb even higher.
It is always easier to get downwards than upwards.
All in all, core team might continue with the company or not. Either way, their influence on the company spirit and way will last much much longer.
Invest in your core team. Make them the best of the best. You wont be sorry about it later.