This has been bugging me recently as I'm sure there's a really simple answer to it, but my Thai isn't that good. Let's say someone mentions plans and rather than just "good idea" or "excellent", is there a way of saying something along the lines of the English "That sounds like a good idea"... or "That sounds like fun...". I suppose I could say "I think that's fun.." - would that be this?

ผมคิดว่าสนุก (?)

But there has to be a more casual way of saying it, yes..?

I'd say น่าสนุก

or how about เอาสิ

how about น่าสนุกดี ?

Agree with chaamlocal and wrelevate.

เห็นจะดี comes to my mind, not sure how it translates exactly.

เห็นจะดี comes to my mind, not sure how it translates exactly.

While the negative ไม่เห็นจะดี is common, I've never heard this phrase in the affirmative.

Anyone?

I would say เข้าท่าดี

Also, I agree on "เห็นจะดี" sounds weird to me

The LUK KHREUNG comedian Chris Wright on his comedy video 'Chris Unseen' had the Thai subtitles for the English phrase 'That sounds like a good idea' as:

ฟังดูเป็นความคิดที่ดีเลย

Is this a good translation? Or does it sound weird to a native Thai speaker?

A bit formal sounding to me, but technically correct.