how interested would you be in a partnership?

based on past experience, not very ;)

that said, your attitude / personality comes across in your post enough that I would probably give you a hearing. (that's intended as a compliment :) )

I'd want to see:

• a business plan (with best/worst case financials). I would be judging your "sanity" based on the level of realism.
• your ability to sell - you're going to have to sell me on a very significant opportunity cost - you're asking me to give up my "day job" to work, presumably for little or no money, on your idea
• how is my rent etc going to get paid before the business generates profit.

More importantly than that, I would need to like you as a person. We'd need to work closely together for probably at least 10 years. Borderline sociopaths with an MBA and / or ex-estate agent types need not apply.

• Don't lie to me (it's usually trivially easy to spot and you're insulting my intelligence)
• Don't waste my time
• Apply basic manners (like thanking me for my time) - this will make you stand out from the crowd I'm afraid.
• Don't ask me to sign an NDA
• Don't say "doesn't it bother you that my grandson could do this"
• Don't patronise me by assuming I fit some techie stereotype
• Don't say "It's like LinkedIn but better. But of course, I can't afford to give up my day job at first".

basic accounting knowledge, basic design skills, in-depth marketing expertise

me too, and then some. you're going to need to be able to sell ;p - and I've worked with some great sales people - and understand the difference they can make. Show me that you're a great sales person too or at the very least have the potential.

Oh, and I would (at a guess) be investing 6 months of my life building an MVP. What are you putting into the ante ... ? (and don't say "the mockups and my years of marketing experience")