It's very hard to say without knowing your photography style and common usage.

I think the simplest explanation of stabilisation is "it's like having a cheap, flimsy tripod on your camera at all times... without the hassle of a tripod". It can be incredibly beneficial, and it can be useless (and a battery drain).

Personally, I shoot a lot of (non-sporting) events with people moving reasonably slowly, and static scenes, and often indoors. So for me I would not buy a telephoto lens without stabilisation, because it would be useful in almost every single shot I will take with it. At 300mm (crop sensor) I can drop my shutter speed from 1/480 (required by 1/f rule) to about 1/60 (for a stationary person). That means a much less noisy ISO of say 400 instead of 3200.

If you're using the lens primarily to shoot sport, active wildlife, or kids/pets running around, then stabilisation won't do as much. You'll likely be shooting at 1/160 or faster anyway, which isn't very far from 1/480 for 300mm (1.5 stops) and you would get no benefit from stabilisation below about 100mm anyway, because, while shooting at 1/50 may result in a nice sharp background, the person running in the image is just going to be a big blur below about 1/160.

If that's too technical, then here are some over-simplified rules to when you would likely NEED, WANT or DON'T CARE about stabilisation:

• Active Sports — DON'T CARE
• Anything on a tripod — DON'T CARE
• Daytime Landscapes — DON'T CARE
• Night-time Landscapes — DON'T CARE (you'll need a tripod anyway)
• Outdoor day-time photography — DON'T CARE (maybe WANT)
• Portraits — WANT
• Bird-watching — WANT
• Indoor events — NEED (maybe WANT)
• Evening photography without a tripod — NEED

The downside to not having stabilisation is either excessive image noise (because you've had use ISO 6400+ to get the shot) and/or blurry photos because there just isn't enough light to let you hand-hold the lens.

Photographers have managed for decades without VR/OS/IS/etc; all it really buys is the ability to get by without a tripod for a bit longer.