Hi, sorry for the delayed reply - okay, the 782s I don't know having never heard them, but another chap on here rates them and has a pair. Not with Sansui gear, but nonetheless, I think they'd be worth hearing.
I listen to a wide cross-section of music and while I'd be inclined to say that the 752 on its own might be a tad on the lean side, partnered with the 717 it works a treat. I'm more rock, but indie and classical do just fine. The crux with any system is the quality of the recording I think - great electronics are all very well, but feed them some highly compressed / over limited / excessively EQ'd stuff and it'll cripple your listening experience before it's started. Get some great recordings (have a look at the Steve Hoffman forum and sign-up to access one of the best free resources on the 'net to help you on your way) and your stereo will sing.
The 753s are apparently superb, the only downside with them - and by extension, the entire 75 series - is that Mission no longer support that product line, which is only an issue if you blow a tweeter or main drive unit. Finding one replacement for a 752 might be easier than finding three or four for the 753 (as it has four drive units per speaker) off Ebay. The slight upside is of course that 752s can be had for around £100 a pair secondhand in the UK (mine were £80) and the 753 is often had for about £200-250, so replacements should probably thought of in terms of buying entire speakers as opposed to individual drive units. The other big positive going about it this way is that as the original selling price for the 752 was around £500 and about £700 for the 753 in the mid-90s, they're likely to have gone to owners who'd be inclined to look after them more than trash them. As with all older gear, there are caveats as well as benefits to consider.
Depending on your budget, there are of course some very good examples of newer speakers out there too, but that ramps up the cost. Certainly, for the price paid for the Missions, you won't find a speaker under £500 that'll better them and I'd imagine for the 752 and 753, you could push that up to £1000 with some justification to spare.
As for the questions - no worries. My views are just views, not gospel, so don't put too much store in them! In any case, the older gear has a lot going for it if you land a winner and you have!