Upgrading OS Question

Dear Friends,

Thanks to this forum, I have upgraded my iMac PC to:

Mac OS X 10.6.8

Processor 2GHz Intel Core 2 Due

Memory:4GB 667MHz DR2 SDRAM

And I am happy with all the performance so far. No complaint, but in thankfulness, as it is still a very good PC. Do you suggest I take a second upgrade to 10.7 / 10.8 /10.9/??

Or just leave it as it is, and keep enjoying it until one day, it is being forced to upgrade?

Any advice will be appreciated!