This is a hard question for anyone to answer for you. First of all, we don't know about your finances. Can you easily afford to buy the Shield, or will it put you in a bind, or will you have to put it on a credit card? If you can easily afford it, that's one thing...if not, you have guns now and you should wait until you can pay cash, and not be strapped in the process.
If you can easily afford it, then the question becomes, will it do anything more for you than the guns you already have? That defines need...but if you don't need it, there's nothing wrong with just wanting it. As long as you can afford it, of course.
Personally, while I think the 3913 is a fine gun, I'd prefer to carry the Shield and keep my 3913 for "nice." Same thing with my 1911s. But that's just me.
So, after giving you all this help, all I can say is that if you can afford it and want it, buy it. It's a great gun...and if you don't enjoy it, then sell it.
