I would surmise that if your current loudspeakers are a full bandwidth design then the only way for you to determine whether they are the weak link is by direct comparison with alternative options. If funds allow you could even audition state of the art equipment to determine where your system might be lacking.
The same would go for turntables /arms/ cartridges and for tube amps if applicable in your case.
In an imperfect world it might be wise to first determine just what you are looking for before throwing any more money at it.
Assembling an audio system is not always a simple case of buying expensive components and hoping for the best. There is nothing like comparison when it comes to audio. You'll know it when you hear it, if you don't then you can pass.