Best way to acquire site that's above me on SERP

Hi, I hope this is the right forum section! Please excuse the ambiguity but "productX" is essentially a product name.

Basically I am #2 in search results for "productX forum", the site above me is only there based on his domain which is literally productXforums.net

What needs to be taken into account is sheer size of my forum over his, my forum has been established for over 2 years and has 50k members. My forum has a popular category devoted to productX which is why I am ranking so high.

His forum however is obviously 100% devoted but it is only a month or so old and is basically not very active at all (less than 200 members).

I am currently in talks with the owner of #1, what I would like to ask is if you think it would be worth purchasing productXforums.net?
If I did, how would I best benefit from it? I am not going to be able to rename my forum and I don't want to separate it either. I'm not too sure but I dont think simply doing a 301 redirect to my productX section will do me much good as the domain will drop off the top spot (thus promoting me to #1 though!)

Would #1 eventually die off the Google top spot due to lack of activity anyway?

Any advice is appreciated

If you buy it, i would suggest parking it on your category, so

productxforums.net => yoursite.com/fourm-productx/

for example. the idea is that eventually this will fall from #1 and put your real site there.