Yes, HUGE improvement in my opinion. The L50 is not much different than the L36, which itself is not particularly impressive. The tweeter in the L50 is the LE26, a paper-cone tweeter from before JBL started using dome tweeters in most of their home speakers. I don't personally care for paper-cone tweeters but to be fair there are some who actually do like them. The woofer is the 127A, the same as the 125A in the L36 but with the dust cap in the other direction. Don't expect much bass from this woofer, and because it uses an alnico magnet, you can potentially demagnetize it if you run too much power through it. The LE5-10 midrange in the L50 is nice at least.
The 4411 uses the 044 tweeter, also used in other speakers like the L112 and L150A. A very nice dome tweeter that has great upper-end resolution while not being quite as "harsh" as some of the later titanium-dome tweeters. The LE5-9 midrange in the 4411 is very similar to the LE5-10 midrange in the L50 but has an edgewound voice coil and slightly increased efficiency. The 128H woofer in the 4411 is fantastic, used in many other speakers such as the L150, L150A, L112, 4412, 4412A, etc. The 4412A using the 128H-1 (same as 128H but with black cone) was sold new all the way until 2006 as the woofer had more than stood the test of time.
So really, you are talking about a very big potential for improvement on both the upper-end and lower-end. Upper-end improvement will depend at least partially on how much you actually like the existing sound you get from the paper-cone tweeters in your L50 speakers. Low-end improvement will be guaranteed however as the 10" 127A in the L50 is nothing compared to the 12" 128H in the 4411. This will be even more true if you enjoy music with a lot of bass.
