The d3100 sensor is pretty old, but there is nothing wrong with it. It may have less MP and high ISO may be inferior to the current crop, but any good lense will give excellent results.
In my opinion, what you should be considering is what sort of lenses are you interested in.
. If you shoot in good light or with a good flash, then you really have no need for high-end lenses. They cost more because of better build, faster AF and higher resolution and can be used in lower light. The the IQ with D3100 will good.
. If they are specialist lenses - macro or TS lenses and you are satisfied with the MP of D3100, then as long as you have good light the IQ does not suffer.
. If you want better lenses for faster AF and good low light performance, then you need to upgrade your body to either D7xxx or D6xx series. If you want large MP then D8xx is what you need.
In isolation a high end lense by it self does not need a better body. It is the type of shooting that may need a better body-better lense combination