I officially learnt piano up to grade 2, and have been learning myself for couple of years, er sort of just playing random pieces i like. But i've got to a stage where I feel like my technique is lacking (especially now since i'm trying to play the heart asks pleasure first by Michael Nyman), and nor do i feel like I'm improving or anything.

Is the only solution take up proper piano lessons again? Any suggestions?

Well it really depends, but do you feel like you need a proper teacher to teach you piano? I mean if you're kinda ok then its fine not to attend proper piano lessons but seriously i reckon professional lessons are good cos if you get a good teacher then you can learn a lot of extra things and you'll be able to get good advice...
Hmmm... how about start taking piano lessons for a little while and if you think its benefiting you then continue i mean there's no harm there :)

Sometimes I play a piece and I would really like feedback and stuff, so i know how to improve or like minor details that I'm missing out. I did originally intend to get piano lessons, until I found out the price, and studies are hectic and so on, so if i really wanted lessons, I would have to plan properly. I've only checked at Yamaha and they don't seem to have individual lessons, so it's like pay for the whole semester or something like that. But trying out a few lessons is not a bad idea...

Hmmm.... do you anyone who teaches or even plays piano? you could probably ask them for a good piano teacher. Or, sometimes if you live in a city with a university or college, some college students are willing to teach. If you attend a high school, you could probably play for one of the music teachers and ask them to critique you...

It's probably better to get proper piano lessons because I have experiences of my own of learning by myself. Learning by yourself is kind of hard but taking proper piano lessons will teach you properly the steps. Yup I think the best way is to take proper piano lessons.:P

You can keep learning and improving by yourself. However a teacher would benefit you by helping with techniques and possible bad habits while playing, and that is something people may ignore if they are learning by their own. Also you would receive advices about how you 'should' play a piece and receive help with possible mistake.

If you gonna keep learning by yourself I recommend you to record what you play and compare it with professional recordings if is possible, to discover what you are doing wrong, what you need to improve, etc. And to try to learn from all the available sources possibles also.

I would say a teacher is recommendable to help you to grow playing piano for avoid bad techniques and habits, but still you can keep learning by your own.

I am more self-taught in every aspects of music than instructed by a teacher and have learnt much more by my own in terms of music generally, but having a teacher have helped me to improve things in my playing that I could have ignored.

Hmm yeah, I was making plans to try take a couple of lessons.. just for a month to try out, and also cos its holidays. Probably when I grad I'll have time to take regular lessons.