I traded in my non WAAS 530 for a new 530W, and installed a new 430 W as
well for around $11,000, including the new antennas and cabling, along with
the installation and annunciator.

The upgrade for a 430 may not be as valuable as for a 530, since the screen
is so much smaller, and there is less information available. Flying an
approach with a single unit, it would not be practical to switch from the
map page to the terrain page and back. The situational awareness from the
530 is far superior.

However, flying the GPS approaches when coupled to an autopilot are a dream-
smooth, and with no hunting like on an ILS. This would be the case with
either unit.

From the SA perspective alone, upgrading the 430 may not be cost effective,
especially with a single unit installation.