Definitely. Is there a huge difference between the core two duos and the new ones? Enough to fork out $1500 or so?
Check out some of the benchmark numbers on everymac.
Benchmarks aren't always 'real life transferable,' but compare the multiple years of the core 2 duo models to the first gen/2010 and then the 2011 macbook numbers. Core 2s did see some changes - faster, cache sizes, drop in process size, but they were within the same generation, relatively minor overall in speed differences. I ran a 6GB Santa Rosa MB for several years, and never really 'needed' to upgrade speed-wise to another C2D system. I would have still been running my original C2D MBP except for the RAM limits there of 3GB - multiple VMs and dev work just don't mix well after a while. :-/
The performance jump to i5/i7 is pretty significant. Of course, if you're a gamer, just a GPU jump is significant, while if you spend most of your time browsing the web, editing a few word/OO documents and presentations, it's probably a waste of $ as you're not going to benefit much beyond the whole 'new and shiny' factor. If you're spending a lot of time at near 100% CPU usage and/or waiting 'a lot' on programs to complete work or keep up, it may be worth the upgrade, but if not, just add some ram for $50 or so and it'll likely give a decent boost by itself, then wait until you're sure you need (or very strongly want/convince yourself) the newer model...and you probably do want to at least wait a few more months to see what the next model lineup looks like, as others have mentioned.
If it does what you need, or will with another 4gb of RAM, it's not broke, so don't 'fix' it.
