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The GPS in the N900 is a TI GPS5030.
Now, TI produces NL5500, the industry’s first single chip that combines assisted global positioning satellite (A-GPS), Bluetooth 2.1 and ultra-low power technologies, as well as FM receive/transmit capabilities. It maximises board space by 40 percent and reduces power consumption by up to 50 percent over previous TI solutions. It also reduces the “time to first fix” (TTFF) over previous TI solutions. Integrated “position optimizer” software delivers superior accuracy in weak satellite signal areas, such as urban centers and heavily wooded areas.

Unfortunately, TI sells the chip only to manufacturers, not to single individuals. However, if somebody is willing enough, he could replace current GPS chip with the newest one, and remove Bluetooth/FM chips as no longer needed, and tell others whether the benefits are worth the trouble.

When there are more satellites in the sky (Galileo should be operational by 2014, GLONASS is operational, COMPASS has 5 satellites operational and 30 planned), GNSS precision will become better. The problem is, you will need a chip analysing all signals (in different codes and at differing frequencies) from all visible satellites to get this precision.

The good news are, at some point you will decide that you don't need:
higher precision
because you have your own eyes,
and +-1 metre isn't important;
faster GPS lock
because you have patience,
and +-1 minute changes nothing;
digital compass
because you have an analog one,
and it's not difficult to learn all the constellations by book
if the weather is good enough to see them;
screen with higher resolution
because it's already too high;
that the large device is better than a small one
which would require a needle-thin stylus.

Any broken part can be replaced/updated, in theory.

USB fragility, absence of USB host mode and upcoming Bluetooth 3.0 can become sources of increasing frustration.