Udon Thani to Chiang Mai by road
 

Thinking of doing this drive.

Fly Udon 1 night
Nong Khai 2 nights
Chiang Khan 2 nights
Phu Ruea 1 night (not sure if Loei town is worth a night)
Phetchabun 1 or 2 nights
Phitsanulok 1 night
Day trip Sukhothai
Lampang 3 nights
Chae Son NP day trip

Good idea or not?

Lampang 3 nights and none in Loei? Only thing in Lampang is the massive coal mine and power plant both of which support the golf course. Loei's not much but countryside is nicer. Main roads good, avoid small highways as often very poorly marked and getting lost will bring misery.

Love Nong Khai.

A great place to stay is The Mutmee, sat right on the Mekong looking across the river to Laos...

http://www.mutmee.com/

...but you might not want to leave.

Jobin, I have planned above 3 nights in Loei province being 2 in Chiang Khan and 1 Phu Ruea. Should I stay 2 nights in Loei town?

If Loei and Phetchabun are more scenic I could end the trip in Phitsanulok.

It's just that some people said they liked Lampang. But if it's just a few temples then could drop it.

Udon to Phits would be about 470km plus side trips.