Polygon count used to the big thing to worry about just 2 years ago, not quite anymore

That doesn't mean you can be reckless but...
128 polys for a jetway is nothing. Maybe you have seen our little TNCM. jetways there are 1000 polys each and the Max source file for that Aiport contains no less then 125.000 polys total. That includes Hotels, cars, taxilines, everything within a few 100m of the airport. Added to the island mesh, autogen, AI and other things you see by default it is safe to assume that FS is easily rendering 200.000 polygons.
Depending on location you can't take it that far, but I would say that 50.000 polys is a completely normal budget for an airport addon nowadays. It hasn't always been like that, just a few years back my older stuff ranged in the 20.000 count.
PS: In FS2004 the tools you use to build your polys can make a huge difference. Make sure the models are Gmax (or anything that compiles with BGLC/MakeMdl), some of the very old tools that compile in SCASM can also generate good results but there is a very old SCASM branch that creates extremely slow content.