What are some good ways to do low level idea validation before you get into the thick of developing a business concept? In other words, I am trying to find a system to prevent my habit of chasing all these great ideas, spending time, energy and money on so many duds. I know about test landing pages, but i tend to really strive to create beautiful design so that to me is already a step too far
The best way to validate ideas BEFORE posting a landing page is to talk to people that would buy your idea. This is really difficult both psychologically and because it means you have to have to find people to talk to... But you will create a much better product because of it. When you talk to people, ask them what their challenges are in the area you are trying to create a product in. You want to be patient and go deep. Another great question is, "If you had a million dollars to make this problem go away, how would you solve it?" See if they tell you your solution; then you know you have a great idea. But if not then you'll have ideas of how to make it better!
Try to discredit your ideas and consider developing the least discredited one.
Even if after taking all the above into consideration your idea is still ‘iceberg-less’ it’s always a good policy to ask an online strategy experts to have a quick look into it.
Group your ideas into increasing levels of technical and business savvy. (a 2D chart where the horizontal is increasing tech, vertical is increasing business)
Talking to typical family & friends is a good use of time mostly for those ideas low in technical and business jargon. Anything else, speak to audience with relevant experience.
If you are such an idea factory churning out mostly equally appealing ideas (thus your lack of focus), choose to execute ideas most suitable with your level of expertise. In fact, execute those few notches below your level for faster time to market.
I know you say "except for landing pages"... but the answer is landing pages.
If you can't control yourself to put a basic landing page up without going too far, I suspect you are in for trouble when you actually try to make a profitable startup.
It is very important to know where to best spend your time, as time is often your most limiting factor. If you can't do it now, it only gets harder later.
Make some landing pages...
Pick one of your ideas that you have as many friends, family and contacts that would be willing hear a quick pitch and see a demonstration.
You've recognized you have a problem in spending too much time making your landing page look too beautiful. My recommendation would be to sketch a wireframe of the site. This may help you avoid this temptation.
I think @Joel is right about going with a landing page, but maybe you just need this intermediate step to get you going.