There's a huge difference between Adam Dicker turning down offers of thousands waiting for the right offer to come along, or not, than you saying that $500 offer you just received is too low and wait for the next offer, which might be 2 years down the line coming, if ever. I would value eBirthdayGifts.com at between $500 to $2000. I'd probably be a serious seller at $1000+, depending on my purchase price. We are all at different levels when it comes what we will accept for the same domain. Us smaller fry, need the cash flow. We cannot spend the time to hype up our domains and wait 10 years for the right offer to come along. For one domain maybe, but not for our entire, or substantial portion of our portfolio. We need the cash flow to turn over. I also think eBirthdayGifts.com is already a tad long. But it wouldn't matter much with great SEO. I would still prefer single to two word keywords.
I think it's almost at random, that you can get lucky with an "e" or "i" prefix. There is no formula. Obviously you need a commercial word(s) to start with. Something that can be monetized. You need huge traffic on the basic search term(s). Then you've got to find a domain with "e" or "i" which isn't already registered. If you've found any, PM me and I give you my opinion. If you don't trust me to do that, that's up/down to you. I am an honest person with a good reputation on NP, which I'm not about to kill over stealing an "e" or "i" domain from you.
It's a niche, just like any other. It doesn't do much harm to have a few of these domains around in your portfolio. I have only ever sold 1 "i"+1 word domain for $750, several years ago. It got me hooked. But they are not fast sellers. So I wouldn't bet the farm on this niche.
I certainly would never have hand-reg eBirthdayGifts.com or bought it in the aftermarket. I think it is an extremely small market (of maybe 1) who might pay 5 figures for this domain. If it was me, I'd go find a better domain, personally. Proper SEO (done by a professional) is and can be a great leveller