Can I use this to fill in the ridges for those 70's faux wood panels on my interior walls? I swear the prev owner gota great deal on wall panels..

No. No filler will do that. Panels are thin and flexible. Even panels that have been glued to walls still flex enough to cause the filler to eventually release. Remove the panels and repair whatever damaged walls are behind them.

This product would not be suitable for your job. Additionally, you have a unique design on your wall in grooves, something that drywall doesn't have. A couple coats of good primer and you can paint your wood paneling. It looks great with the vertical grooves. (We did this with our house) Don't replace "old" with "new and junky".

Because this product has a sanded texture it will likely not be a good match to the existing surface. Likewise, the product does not sand well, which means that the product must be applied and smoothed prior to drying, post application adjustentmentioned are not practical for large areas.

I would say YES it would work , but it would be a heck of a job. The first point is you would have to make sure that you put it on fast then used like a trowel to make sure that it was really smooth NO bumps. This stuff dries fast, once dry you would have to use a primer or a paint with primer to cover it well. The fill will be like cement when it dries, so keep that in mind too, the texture will not be the same as the faux wood. But I don't see any reason why it wouldn't work.