I take it you live in the UK? Here's another way to look at it.

I have 20 nights to see the British Isles, so we're thinking of flying into London and then going to Dover, a night or two in Edinburgh, and see Loch Lomand and Loch Ness. We would love to see the Beatles sights in Liverpool. Then visit Wales. We'd also like to spend some time in Dublin and drive the West Coast of Ireland, and of course see Belfast and the Giant's Causeway.

OR

We're thinking of exploring Devon and Cornwall after London. We'd also like to work in the Southeast Coast and possibly Wales. We have 20 days to do this.

Your original plan is not unlike the first above. The second would be more like visiting Cape Cod, Boston, New York, and some of New England.

I guess it depends on whether you want to "see" a lot of things or "experience and explore" a few.

Hi NeopAtrick, we live in England, this will be my 11th time to the USA but only the second for my husband, so we're trying to cram in as much possible so wanting to see a lot of things.
I guess I kind of look at it as, there's 3 very heavy driving days, we will try our best to make them as enjoyable as possible, good snacks, local radio and music, and each other for company, and hopefully some great countryside! Hopefully 3 out of 20 days heavy driving won't feel like it's eaten into our holiday too much, we will see!