I would try a set of Gator Mulching Blades first (cheapest option), and if still don't get the desired results go for the mulch kit. Buying a whole new deck is a little extreme. You might also ensure that your deck is leveled correctly.

I have a mulch kit on my Simplicity Conquest with a 44 inch deck. It works well as long as I clean out the deck especially if I happen to cut when its been a bit wet.

In the fall the mulching kit works wonders, I never have to rake / blow leaves anymore.

I'm dealing with a JD 42 not a 48 deck, but in my opinion, the dedicated Freedom mulching deck is well worth bother/cost. It just does a great job, but has about zero suction so it is poor on leaves and other droppings. I got my JD LT160 with the Freedom deck, and then bought an almost new 42C side discharge deck on Ebay from a dealer in PA. It was traded in for a Freedom deck and sold cheap - about $200 delivered on a pallet in MA. I added a new bagger only because i couldn't source a decent used one, and that takes care of all of my spring and fall clean-up. Then I put the Freedom on around first of may and will take it off after the next few weeks, as the leaqves start to drop. If you browse Ebay, you can often find JD decks going cheap - either freedom or side discharge. With a 3 blade 48, there may be bigger differences in performance, although I understand that generally, They don't cut as well as 2 blade, and need power baggers.

We have two mowers for our property which was formerly pasture, a JD LT 160 with the 42" Freedom mulching deck and a GX335 with a 54C deck, mulch kit and Gator blades. The GX335 has been set up this way since the day I bought it. Here in western Washington we generally mow once a week in the spring gradually stretching out to every two weeks in the height of summer. I find that we can avoid clumping and have a neat looking lawn as long as we mow at the correct height, and we're now nearing the end of our fourth season with this equipment. After I mow that first strip across the edge of the field, if there are any visible clippings, I just raise the deck height a notch for the next strip.

There is only one area where I sometimes have a little trouble because it is a north facing fairly steep slope that is in shade most of the day and almost always wet. But even here it comes out okay as long as I don't try to cut too low. We have no trouble mulching leaves with either deck, though we don't have a huge amount of deciduous trees.....just some alder, birch and cottonwood. We never rake leaves and we don't ever use a bagger.

Between the two, I would have to say that the Freedom deck does a little nicer job than my 54C deck. But if I were in your place I would do like Metal suggested. Check to see that your deck is properly leveled and try Gator blades first. If that doesn't work well you can then decide if you want to try the mulch kit.