I would like to have all the latest Infinity Engine stuff like high resolution modes, highlight items feature, updated game mechanics etc. But I would like to save hard drive space (yes, it matters to me) by avoiding putting all the games to it while I only seek to play the original Baldur's Gate now. Is this possible to update the engine to the latest version without installing the newer games content?
High resolution modes are possible in BG1 without BG2/BGT/Tutu by using The Widescreen Mod.
The problem then becomes the GUI, which does not stretch to fill the screen. This can be fixed somewhat with TWM_GUI. The problem with that is it adds some really ugly background images to the menu screens in the game - unless you enjoy inverted maps and SPAAAAAAACE in your Baldur's Gate.
Highlight items is only possible in BG1 if you have BG2: Throne of Bhaal and use Tutu or BGT, unless there's a mod that adds this functionality to BG1 that I'm unaware of.
As for game mechanics, which ones specifically are you missing? A number of things changed between BG1 and BG2, some of which you may be able to find mods for (such as multi-class grand mastery). BG1 Tweaks may be what you're looking for. I'm not aware of a mod for BG1 that adds dual-wielding though.
If you can afford the disk space, you should probably install BG1 and BG2:ToB, then install EasyTutu, then delete your BG1 install. In order to use Tutu BG2 has to stay on your drive, but BG1 doesn't.