A few more thoughts...
I'd agree that it's important to work out what you want to use the bins for and establish what specification is likely to suit. for example, 8x42 is favoured for bird watching (my main use) because they have a good balance between magnification and steadiness, and the light gathering power is pretty good (birds often settle down to roost as dusk is coming in, so conditions can be a bit dull). During the day, 8x42s give a nice bright image, and are excellent for looking into dark areas (such as amongst trees). Compared to the naked eye, they really are light amplifiers.
There is also the basic type of bin to consider - roof prism or porro prism. Roof prism is the more modern type with straight tubes, and porros are the traditional configuration with the dog-leg shape on each barrel. Porros are easier to design well optically, but are bulkier and can be heavier than a similar spec roof. They're also less likely to be waterproof (harder mechanics to protect or seal, I guess). I'd be tempted to think that older porros, of any quality, are unlikely to be waterproof. Nearly all modern roof prism bins are o-ring sealed and purged with nitrogen (= dry gas), meaning that they will never steam up inside due to temperature changes and won't get wet inside if they get rained on or dropped in the proverbial stream.
To get a similar optical quality from roof prism bins means designing in more corrections, and using suitable types of glass where needed. Apparently, something called BaK4 is needed for the prisms in roofs, and the coatings on these can have an effect as well - so-called phase coating helps with accurate colour balance. Similarly, the anti-reflective coatings on the various optical elements can help to increase light transmission through the glass. Lens coatings come in a few forms: coated, multi-coated, and fully multi-coated. Coated means a single layer of coating on the outside surfaces of the external bits of glass, multi-coated means several different coatings on the outside, and fully-multi-coated means all glass to air/nitrogen surfaces are multi-coated. For a given standard of coating, fully multi-coated will give the best light transmission. BaK4 prisms with phase coating will help make things that bit better as well. When I was shopping for decent budget bins a couple of years ago, the Sierras were my choice because they got good reviews, and were nitrogen purged, fully multi-coated and had phase coated BaK4 prisms. In terms of reputation and the main technical spec, they looked good, and I'd say they matched or exceeded my expectations. In a sense, given the difference in price amongst the budget bins, I felt that what they offered was the minimum spec to go for (they were £74 when I got them, and can still be had for £80 or so). Hardly worth saving £10-20 on a cheaper pair, especially if ordering online and not able to try them - my approach was to get something with good comments, and that ticks as many of the technical boxes as possible.
A couple of things stood out when reading binocular reviews when I was shopping. Nearly everybody says their bins are great, but don't go into any substantial detail about why they're great (often, they've upgraded from something cheap and nasty, or simply don't know any better and are talking about their first bins). When reading the more serious reviews, such as by people that take an interest in bins and review lots of them, one comment tends to predominate over all others - the budget bins coming out of China just get better and better, and it is continually surprising how good they can be for prices that would have been unheard of 10 years ago (or even 2 or 3 years ago). Having used the Sierras and Endeavour EDIIs (both Chinese made), and spent some time with the aforementioned Leicas and Swaros, I would tend to agree - the balance between quality and price is very good indeed. So much so, that I'd seriously wonder if an older pair of Zeiss, say, really represent good value, not to mention any appreciable increase in optical quality, compared to what can be had new (or recently-made used). Basically, binocular technology continually moves on as new designs and materials are developed, and the standard of manufacture in China gets better and better (the current cheaper Zeiss bins are made in China, incidentally).
A further comment about chromatic aberration: It seems to be affected by whether the eyes are on-axis with the lenses. I find that if I move the bins sideways a little, CA increases, and that it can be reduced if I adjust the positions of the oculars to find the sweet spot where it's eliminated or substantially reduced. To me, this suggests that there is an aspect to the ergonomics that needs to be kept in mind - bins with twist-up eyecups are easier to get into the right position, especially once you're used to them. I tend to nestle mine into the tops of my eye sockets, pressing lightly on the bony parts under the eyebrows. For spectacle wearers, getting this alignment spot on by feel won't be as easy (the eyecups are twisted down, and the rubber part presses on the glasses, so there isn't the same physical alignment thing). As a non-specs wearer, I also find the twist-up eyecups brilliant for getting the bins at the right distance from the eyes - very easy to lift the bins up, put the tops of the cups under the eyebrow bony parts, and they're nearly always in the optimal position for eye relief and axial alignment. Having used this type, I simply would not consider using the older/cheaper types that don't have twist-up eyecups.
It might help, Dave, if you were to describe your expected uses for binoculars. It's important to keep in mind that they are all a compromise of one sort or another, whether that be optical quality against price, or magnification against shake (or subject size when viewed through the bins), weight, size, ergonomics, etc.
