Upgrade entry level or start over?

You can upgrade your cartridge first if you want to hear immediate improvement without spending much (if you don’t want to upgrade your turntable). When you drop numbers here it’s really nothing. Even if you will spend over $1000 on a phono stage you will hear only your cartridge limitations. Not every cartridge for $300 is good or better. 

Let me take a different approach. Looking at your system I think I would pick a different upgrade path. The LS-50s are well respected but I have a pair and they lack air and top end detail. I think I would look at other speakers for the best upgrade for the buck. 

Thanks for all the responses.

I think I will upgrade the cartridge and phone stage for now. I'm not in a hurry, so I'll be keeping an eye out in the classifieds for a bargain.

Good variety of worthwhile upgrade suggestions.  Any one of them would result in sound quality improvement. I believe that a better quality phono stage is a very good move. As I think it is the "weakest link" bottleneck item in this audio system. 
Good luck, 
Charles 

This is the very reason why I find vinyl so frustrating, it takes considerable money to make a noticeable impact. I've read in many phono stage reviews that it's nearly impossible to find a fully capable phono amp for less than $2,700.00. I'm not so certain whether or not this is true but will say that in relative terms, investing $3,00.00 in a phono amp. cartridge and turntable would be considered 'budget entry level'.

I agree with those others who believe that your focus should be on a better phono amp. I believe the chain towards improvements goes; phono amp, cartridge, tone arm, turntable but this could be an over simplification. The question is whether or not you'll really notice a difference between your current phono amp and the one you'll be able purchase for a $1,000.00?

So if you go the phono amp route, then I'd say try buying one that's used with a rating of 8/10 or above. My phono amp is an ASR Mini Basis Exclusive and is a really good phono amp for its price range. I've seen older used models of the ASR sell for about $1,500.00.