buy plane or get instrument rating?

Hi everyone. I have about 100 hours in 150's and 172's. I am thinking
about getting an instrument rating and buying my own plane within the next
few years. Should I go for the instrument rating first? I was thinking
this might help me build some more time, and the instrument rating would be
looked upon favorably by insurance companies when the time comes to buy.
Or, should I just buy the plane and fly it to get the instrument rating? I
am considering a 172.

Thanks for all advice!

Matt