Hi Omar, I am coming to this post linked from your blog.
This is an excellent subject that does not get discussed enough.
I've been doing private landing pages since the day I started, because I wanted to know everything about visitors from the second I own a domain.
It also forces interested parties to reveal a bit about themselves when inquiries come in.
My advice to you would be analytics, analytics, analytics.
Make sure that you tie your pages in with analytics, so that you know where your visitors are coming from. If you use Google Analytics you can also view the 'network domain' that someone is on while viewing your landing page.
In most cases, the network domain will be 'comcast' or 'verizon' etc... however when corporate entities are using their private networks that information will be shown under the network domain information.
I've received inquiries offering me $300 from a trash gMail account, and then have seen that the same day a single visitor from a specific corporate entity visited my landing page.
To make contact, I provide an eMail address that is displayed in an image (preventing spam). So if I receive an eMail, that same day I can look at my analytics for that day and see all available information on them.
You can also use a form to accomplish this. When someone submits a form you can have some kind of location script installed that adds a hidden field to your form submission that provides you the persons I.P. and location.
As for your wording, "May be for sale" is the right course to take. So many UDRP's are lost because the domain owner is trying to actively sell the domain versus actually using it. "May be for sale" provides you a veil of protection against that.
My landers aren't beautiful, they are very stark and plain - except for the DN name itself. They are functional and get the job done. It's my personal opinion that the name sells itself, and the interested buyer should be able to use their imagination to envision their own use for the name. So as much whitespace as I can provide on a landing page, I will. (yes I like psychology)
I will be interested to see how you fair with your experiment, I wish you the best of success with taking this on.