The keyword here is 'investigation'.
At face value, this domain seems to have no use and no value whatsoever. It was parked almost the entire time it was regged, zero development.
When a domain has zero development and a lot of traffic, the red flags are 'where does that traffic come from' and 'why bother to send a lot of traffic to that site when it's not developed'.
WaybackMachine took many snapshots of this site, dozens each year it was regged. For a parked site? It doesn't even take nearly that many snapshots of any of my websites, and some of them are well developed. Also, all those snapshots are blank. Even a parked page will show up on a few of wayback's snapshots, while the rest will come back blank. But for this domain, I couldn't find a single snapshot that wasn't blank. Very strange to have literally hundreds of snapshots for a domain and every one is blank.
And for a domain to rank so high in Alexa, almost immediately after registration, and with no development, and to remain so steady for years, with no development, is extremely fishy. You don't just reg a meaningless domain, in dot info, and then magically start receiving hundreds of thousands of visitors... who don't even type in that term in English.
You mentioned that you might want to 'not mess with what is working'; things might be working right now, but it's important to investigate what's happening. If you're making a bunch of ad-based income on this domain, and later you find out the traffic is driven there by shady/illegal methods (methods that go against your ad provider's TOS), then it'll eventually be discovered and you'll start to enter a world of problems and possibly litigation.
The huge red flag for me is: someone spent a good deal of energy driving tons of traffic to this domain, apparently only for the purpose of making cash via parking ads. Then they let the domain drop after 4 years. If it's receiving so much traffic and making good income... why did they let it drop? People and corporations literally spend tens and hundreds of thousands of dollars to get their websites such good traffic that they receive these Alexa rankings... the previous owner somehow does that, and then just drops the domain?
Everything about this domain yells out trouble, to me.
It might not be. It might be fine. But all the signs point to a trouble domain, possibly used for phishing or scams or perhaps a lot of blackhat backlink building, I don't know. With fishy domains like this, you investigate to make sure you're not inheriting a bunch of trouble that the previous owner is running away from (that's often why they let such a domain drop), and you investigate to find out how stable and whitehat the traffic is. If you sell this domain for a lot of money to someone, based on traffic and income claims, and then a week or a month after that the traffic 'scheme' (if it was a scheme) implodes and their traffic instantly dies down to 10 uniques per month - which is what it should be for this domain - then you've possibly got a lawsuit and more problems.
Investigate, so you know what you've gotten into. For starters, email the .com and .net owners, ask what the heck this domain means, ask why it has any meaning to the Chinese, ask why it might receive so much traffic? Especially when the .com is simply parked for sale and the .net is blank? How come the .info is receiving so much traffic?
Good luck
