Tips for an old previous and renewed embedded programmer
I've been doing embedded system design for the last 35 years (I'm just a couple of years older than you), and currently have projects going on using 8-bit (Silicon Labs 8051 and Freescale 68HCS08), 16-bit (Microchip 24FJ and dsPIC33FJ), and 32-bit (TI TMS320DM365) processors.

The 8-bit chips are probably going to be what you will initially feel the most comfortable with, and are still fun to program in assembly in addition to C.  The 68HCS08 is an update of the Motorola 68HC05 line, and I particularly like its instruction set (not as nice as the old 6809, which was a wonderful processor to write assembly code for).

Compared to the old days when development boards and associated ICE's cost hundreds or even thousands of dollars, you can now get pretty decent evaluation boards for under $100, and free compilers.

Just for fun, I recently bought a development board for the Parallax Propeller chip, which has 8 cores (Parallax calls them "gogs") that run in parallel.  All I/O is done in software, which means with very little external hardware the chip supports things like PS/2 keyboards and mice, and VGA output.  There is a demo board available for $80.  (I have its big brother, which is currently on sale for $150.)