You do mean that you traded a 2013 2.5 SV for a 2013 3.5 SL...correct? You must have bought one of the very first cars that were available to have had it for a full 5 months.
I totally understand wanting the V6 over the I4 engine. That's why my pre-order in June was for a 3.5 SL, sight unseen. In my opinion, the two engines result in two cars that are totally different in character. What I mean is the refinement
of the V6 in terms of low noise, smoothness (no engine vibration), and abundant torque (meaning really effortless acceleration) is the reason why Nissan offers the engine although it expects no more than 10% of buyers to take the V6. Nissan wants to compete with the Toyota and Honda models that still offer a V6, so they offer one too. What they've done for 2013 is push the car upmarket without pushing up the price (much). They know that the new Altima will cannibalize some sales of the Maxima, at least until they release an all-new Maxima, but believe me the salespeople who are pushing both cars right now are carefully positioning the two cars at opposite ends of their parking lots. I've owned two Maxima's in my life and I loved both of them. But, I don't own a current model because it seems overweight, over thought, and way too pricey to me, particularly considering that you can now get an even better car (not trimmed quite as well, but dynamically much better) in the Altima. That's why when I heard that Nissan was building an "upmarket" Altima for 2013 I decided to put in an order for one and trade my 2008 Altima Coupe (3.5 SE).
Oh, and considering the cost of the extra equipment in the SL over the SV (regardless of engine), I think the SL is a superior value. With the 7 trims available for the 2013 Altima, Nissan is covering all bases and price points (i.e., the difference in $1000 or $2000 is a deal breaker for many folks). The leather trim, Bose radio, xenon headlights, heated seats (and steering wheel and mirrors) make the SL Altima into a car that can compete with (some of the) cars from Acura, Lexus, and even BMW. (I don't talk about the Koreans or American cars in the same breath as the Japanese and Germans because in my opinion they both still have a long way to go to be comparable.) But I digress....
In closing, I want to be clear that I think the 2.5 I4 is a nice, impressive car--for what it is. That is, if you value MPG and don't care so much about engine refinement (i.e., noise, reserve power) and want to save $1200 to $2000, then the 2.5 is a great buy. But, if you want an Altima that compares very well with cars that cost many thousands of dollars more (like the Maxima), then I suggest that you spend some time in the 3.5 model (and the only one that matters in my mind is the SL) before plunking down your cash. I'm just saying.