One reason not to retire the shuttle concept.
A large shuttle type vehicle will be needed if we are to have a serious manned presence in space. Its ability to carrry and retrieve large cargo is a must for orbital construction. Such a capability must not be lost.
I suggest scrapping the Ares I and developing the Ares V as a mullti-purpose launcher. Design it to be able to carry payloads on top or piggybacked on the side. Then it could launch manned capsules, lunar landers, modules, deep space probes, and a new Buran style orbiter. By removing the burden of being the launch vehicle itself, a next generation shuttle could be designed and built as funding permitted.