Surprisingly enough I don’t think the big displays account as big a current draw as we might imagine (and their drain is partially masked by improvements elsewhere). For example the Elecraft K3 draws about 0.9A on receive which is very close to that of the original IC-7300.
The IC-705 has a screen similar to that of the 7300 but, being meant for portable use, it’s easy to turn off display to help battery life. I can’t find the figures at the moment but it didn’t help as much as I’d expected.
That’ll be part of it for sure but the SDR digital front end is probably the main culprit. A serious amount of processor power is needed, even for the 7300 which is (still) only a 14-bit A to D. This is a problem for all battery powered radio systems, so there is huge ongoing effort to improve processor performance vs. power consumption. I’m guessing that is at the heart of this reduction in supply current.
If I can manage IC9700/p I’m sure you can manage an IC7300 
I surmise that the release of the mk2 version has led to people trading in their mk1s, a well-known supplier has several pre-owned mk1s for sale, priced substantially lower than they would have been several weeks ago!
I must admit to not really understanding this. 7300 is a fine radio. 7300mk2 is better. But if you want a better radio do you not really want a “much better” radio? I wouldn’t have thought it worthwhile.
Some people just want the latest thing all the time - cars, bikes, trainers, HF transceivers…
I suppose I’ve spent too long doing cost<>benefit analyses Pete to just spend money on the new one because it’s new.
I suppose it is bragging rights (rites? ) at the one extreme of the boy’s toys syndrome. I guess I am at the other end, I enjoy driving a rig that is nearly fifty years old!
I tend to agree. The 7300 was and remains an astonishing achievement for its price point. It’s a decent radio but it is rather too easy to overload on large antennas due to only being a 14 bit A>D. The MkII is also only 14 bit so this will still be its Achilles’ heel. 16 bit full SDRs tend to be a lot more expensive but worth it if your usage case can justify the cash. Full disclosure: I had one of the first 7300s and was suitably impressed but my big Yagis at home demanded 16 bit dynamic range.
Or old, good superheterodyne 
Looks very interesting upgrade,but if one alreadys has one ther eis no point in buying a mk2.
If nothing else,next year at ham radio there might be a surge of used 7300s mk1’s for sale. Hopefully for a decent price. 
73 Karlo