I would agree with most points you make in your last paragraphs and certainly the last one.
I would tend to say that it is too easy to be critical of using particular modern words like rapture and trinity that are - of course - not written themselves in the texts. A quick off-the-cuff reference to what Christian's term the trinity that comes to mind would be the description of Christ's water baptism by John. I would truly be curious to hear an alternative interpretation for 1 Thess. 4:13-18 that is not consistent with what modern Christians term the rapture - regardless of when the church in its history started to think about the meaning in that particular way. To dismiss the spirit of clear non-symbolic passages (as opposed to clearly figurative passages) because of words Christians have tagged them with or how long it took the church to figure it out, or how long it was forgotten by the church when it was understood by the early church just seems wrong.
I don't agree with 100% of the Left Behind theology - it is a work of fiction. But I do think they did get a better than average amount of the prophecy correct, which isn't easy. My biggest issues with their texts would be the extent of the antichrist's kingdom as I think the prophecy would limit it to the extent of the Roman Empire, and I take exception to their mark of Christ/mark of the beast symbols, but overall not a bad attempt to put into readable form a couple of tough books of the Bible to read in most translations. Is it better to try to read and understand the originals? Yes, of course. But most people write off much of the Bible prophecy because they don't have the time or background to try to unravel it. The fact that it is spread over many books some of which refers to near term events and some yet to be fulfilled doesn't help. So while I'd rather people read the best translation of the original they can find, I don't find the fictional texts to be a problem. As you say - people read things many different ways and it will be interesting to see who is actually right or wrong about Revelation interpretations. The important thing is the eternal end point and not a scorecard or grading of unraveling prophecy before hand. And, of course, focusing on the big things would promote unity. Trouble is, agreeing on what the big things are is just as hard a thing to do as getting unity on them.
I suppose that people could take the approach you suggest about the rapture and the planet and not caring about it since it will all pass away. I guess that to me, God Himself is going to beat the planet up pretty hard according to Revelation, so I'm not sure that what we do is going to be noticed. But I would also point out that regardless of the rapture, the timing of it is not foretold. So doing whatever we wanted with the planet would seem to be a pretty silly thing to do - even if we thought it was going to be happening soon. After all, the early church thought it was going to be happening soon as well. We were originally created to be caretakers, and I'd think this should be our goal with respect to the planet itself. Jesus projected a pretty good "waste not" philosophy while on the earth.
As far as the rest, 1 Cor 13 is a pretty good summary of what to shoot for.