The tires on my 240 are probably 4 or 5 years old. They're starting to get some cracks in the tread, and a few small ones on the sidewalls. The sidewalls have a little 'wave' in some spots, as well.

I have to drive 300 miles or so this weekend. Should i get new tires tomorrow?

What kind of tires should i buy? (I run snows in the winter, so no all-seasons necessary)

Have you noticed any changes in drivability? Any vibration or anything like that? Where will you be driving? Middle of nowhere type places where you'll be screwed if you blow out a tire, or populated areas where you could find a tire store if the worst happened? If its the latter and you havent noticed problems, I'd probably put it off (but I put off a lot of things). If you'll be in the middle of nowhere, it might be worth taking the time to get new tires, youll have to do it sooner or later anyway.

If you live where it is hot and / or the road will get hot or you are doing a long drive , I would change the tires for sure . I lost a tire that was just like your (well , maybe I would need to see it but it sounds like it)

You've got about a year to go, according to recent tire industry and safety organization findings. At about this six-year age, tires start to deteriorate from the accumulated effects of U.V., heat, etc., and it's often recommended that tires be changed at this age even if there's a lot of tread left, simply because the "carcass" (the underlying plies, sidewalls, etc.) have reduced capacity to perform.

So at your tires' age, I'd wait a year unless you see signs of some breakdown. Maybe you live in a region with more abusive road conditions, or brighter (more damaging) sunlight, etc. This six year figure is just a guideline, and your tires may be in need of replacement sooner, or later.

But at least you're taking a look at your tires, which is more than I can say about the vast majority of folks.