Of late I\'m facing the issues that points finger to VC6 compiler.
Few of them are:
The no-brainer answer is yes, and ASAP. You have free alternatives like VC++ express and Code::Blocks, if the cost as in issue. The pain in solving compatibility issues is IMO no reason not to upgrade because you will have to do it some day anyway and it only gets harder.
The only reason I see for a possible obstacle is if you have MFC code that will be difficult/time consuming to port. In that case you can't use VC++ express (no support for MFC) and you have to make the investment for at least the VS std. edition. That will cost you about EUR 300 (depending on where you live).