Maybe this could be made into general files size talk? Quite interesting research I came up with anyway.
I looked into it and while this is in no way scientific research, it compares the two games on a very even ground.
Here are the raw numbers of what the data contents of each disc combined add up to.
Shenmue: 2006 MB
Shenmue II: 3631 MB
The difference is not quite as in the rereleases but Shenmue II is still about 175% of what Shenmue comes in.
One thing to consider in these numbers of II is that they include a pretty big chuck at 304 MB for the Digest Movie and Saturn video, with the former taking up 207 MB.
I highly doubt that they include Shenmue the Movie. It doesn't make sense to include it in a collection that already has the very game it was used to "replace" earlier. Then there is the very likely scenario that the movie is it's own licensing beast.
With higher data compression, the extra room that Shenmue II takes, it would be possible to include this feature length video in there but what is much more likely is that they encoded the Digest Movie and possibly Saturn video, in a higher resolution and bitrate, so they actually take a lot more space than before even. Or we could just dream that there is MORE bonus content in there.
Comparing the file sizes of the originals and rereleases again, it doesn't seem too overwhelming how much bigger they are, if you take into account that they are dual audio and that the voice recordings always took the biggest part of a disc. This is of course based on the theory that they did it like Xbox port and keep every disc folder intact and just throw them together. Gives a lot of duplicates and further copies of files, wich is of course not very efficient at all, but apparently the easiest solution to get things done. After all they already went that way.