1) Not qualified to answer that
since the highest I have been is a Premier Silver. As a Premier Silver though i got upgraded from GEG (Spokane, WA) to DEN on an Complimentary Upgrade, and got upgraded from SEA to IAH, but then the aircraft changed and so did my upgrade.
2) Yes, there are plans to bring Wi-Fi aboard
http://pss.united.com/web/en-US/cont...i/default.aspx
"Inflight Internet is being installed on additional aircraft beginning in 2012."
3)I have the Explorer and it has perks which are good if you are a general member like Priority Boarding, which is after elites, Primary Rental Car Coverage, Two UA club passes/yr, Baggage Fee waiver for the first bag You +1 companion, the 40-60K bonus miles depending on which deal you find, and Chase is actually giving 50% more bonus miles for purchases between March and April. Also, i dont know much about it, but you can get Complimentary Premier Upgrades for Award Tickets.
4) No, you are only on the upgrade lists for United, but you can use miles to upgrade on some partner airlines.