Game was running fine months ago, I leave it alone, come back... now it won't run
 

That's basically he gist of it.

Now when I try to run SH3 I get an immediate "Silent Hunter III has stopped working" message; it seems to point to the d3d9.dll as the culprit.

I have not fiddled or modified any of the SH3 directory contents since it was all fine-tuned and running perfectly a few months ago with no issues (thanks to you fine folks here).

I have the following Mods:

GWX - Captain America's Officer Icons
GWX - Enhanced Damage Effects
GWX - Merged Campaign
GWX - Integrated Orders
GWX - Main movie - 'Das Boot'
GWX - Axis Mediterranean Aircraft Skins
GWX - English Nav Map and Grid Refs
GWX - Open Hatch Mod
GWX - VIIC41 Player Sub
M.E.P v3
M.E.P v3-Patch
MEP v3 VisualSensors for gwx3
M.E.Pv3 VisualSensors-GWX3
FlatSunFix for M.E.P v3
FSF for M.E.P v3-Patch
Merchant_Fleet_Mod_3.2
Rbs1_SH4_Effects_GWX_30_71
Rbs10-enhancedoilexplosion
MaGui F
TorpedoSolutionButton for MaGui F (NYGM-GWX-WAC)

Could it just be that I've updated my graphics drivers since it last worked and now they're simply incompatible with the game?

Should I reinstall DX9?

If you have updated your video drivers then roll them back to an earlier version and see if that works.