Not to jump down your throat, Indy... but I think this is EXACTLY the type of well-intentioned vaguery that, if it is also occurring at LucasFilm, is going to get us an unsatisfactory Indy 4. It's not that I disagree with any of points you made, but I think it's harder than you think. The thing that stuck out the most to me is your statement "true to the spirit of the other three films"...
What spirit is that? To me, the films are varied at so many levels, that I don't know if there is one "spirit"... Unless that spirit so generic as it will be difficult to define the films in a way worthy of emulation. It is these kinds of generalities that make me nervous about Indy 4. As an example, I will cite the Indy video games. "What's wrong with them?" you ask. Well, they seem to have all the right elements: Indy, artifact, international travel, traps, puzzles, combat with competitors, encounter with the supernatural. But that's just it... the games are "Indy in general." They're TOO general, there's nothing to make them stand on their own and that's why I don't find any of their stories to be very compelling.
Besides the stuff mentioned previously mentioned and all incredibly absurd things (like cameos from the Muppets, or a Hillary Duff soundtrack), I'd like to see the Big Three avoid some subtler pitfalls.
What concerns me most is their treatment of the Jones characters in the 1950s. The two temptations here are either assuming a) Indy hasn't changed at all or, b) he's waning into a fussy old guy obsessed with one or all of the above: his age, obsolescence, or retirement (IE ?I?m getting to old for this shtuff.?) Given the mighty leap in timeframe from the original films, it?s obvious that the world that Indy inhabits has changed... I?d like to see a thoughtful and intriguing change in the character as well.
Also, given the change to the fifties era and the move from WW2 to the Cold War, I would just like to voice my distrust of simply making the Russians the bad guys. I?m not saying it categorically couldn?t work, but I just think it?s too simplistic, too clichéd, and too easy for standard-issue American sensibilities. It just sounds LAZY to me. Pitting Indy against some evil organization that has legions of brainless thugs for him to mow through is a convention that the video game developers will appreciate, but not what I want to see in the film.