Admittedly, as my username might suggest, I am somewhat biased when it comes to the .40 S&W cartridge, but I must say that despite persistent assertions by many that it is a dying cartridge which will soon fade away into obscurity, it remains to be in the top 3 cartridges in terms of sales on most websites, and the sheer amount of folks who bought .40cal pistols due to the sheer amount of low-priced yet high value police trade-ins on the market, I would be so bold as to say that .40 S&W has never been more popular yet more accessible as it is right now.
Besides, even if the .40 S&W cartridge was dying, the fact remains that because most .40cal pistols can be easily converted to 9mm Luger or .357 SIG with nothing more than a drop-in conversion barrel, most .40s you can buy could be easily made to fire other cartridges as well!
So yeah, if you can find a good deal on a .40cal pistol, (which shouldn't be too hard, since PDs continue to trade in their .40s) then I would highly recommend getting one.
Heck, shop around online and you should easily be able to locate some .40cal police trade-in Glocks, SIGs, or S&W M&Ps somewhere at a great price. So yeah, it gets my vote.