The parks will have started to transition to their Spring Break season schedule, meaning slightly longer operating hours (i.e., 9:00 am to 10:00 pm for DL and 9:0 am to 9:00 pm for DCA). EMH is going to be in DCA on Monday, March 9, so RSR and TSMM will both already have fairly substantial lines at opening.
The schedule (subject ot change without notice) is posted on
Disneyland.com:
https://disneyland.disney.go.com/calendars/day/2015-03-09/
If you haven't been there since 2008, I would make a point to check out Buena Vista Street and Carsland in DCA. Both are very well done and fun to check out. RSR (in Carsland) is one of the most popular attractions in DLR. It does have a single rider line (if you don't mind riding separately - you will be separated in the SRL) and FP (I'd get one within the first two hours of park opening). TSMM is probably the second most popular attraction in DCA, but it does not have a SRL or FP. It's a lot of fun, but the line can be long.
Over in DL, there aren't any "new" attractions per se, but some things have been modified since 2008. I think Star Tours debuted the "The Adventure Continues" version since 2008. Big Thunder also underwent renovation recently. Arendelle has been added to Storybook Canal Boats and the Alice attraction had upgrades installed recently.
With only one day, I'd be tempted to recommend skipping F! because it hasn't really changed in terms of the storyline. The new dragon debuted in 2009 or 2010 and is pretty impressive, but F! does require a time commitment if you want a good spot. Neither WoC nor Fireworks are being presented that day, so you don't have to worry about those.
In terms of dining, with only one day, I'd probably stick to counter service to avoid losing an hour to 75 minutes on a TS meal. I highly recommend French Market or Plaza Inn for meals and Jolly Holiday for snacks.
