Are internal component upgrades worth it.

Any modification you try should be something reversible in case you don't like the results.  Any change in the sound could b for better or worse and there is rarely anything that would constitute a universal upgrade.  While often praised, I know folks who don't like the Crites crossover upgrades, for example.  Making a box more rigid does not necessarily improve the sound (not all box resonances are "bad"), and even if bracing the box is a positive, you will probably want to make some other adjustment, such as changing the amount of internal damping material.  It is really a matter of tuning, which means trying different adjustments.  Note too that adding bracing decreases the internal volume of the cabinet and that changes the tuning.  As to upgraded parts, the biggest difference will be the choice of capacitors in the crossover, and again, you will have to listen to the results and be prepared to reverse the change if it is not an improvement.

Another completely different avenue for improvement would be to consider a different amplifier.  The Cornwalls are good candidates for being driven by low-powered tube amps.  The sound of such amps might be something you will like, so you should at least try some low powered tube amps with your speakers if you can.  In most set ups, 40-50 watts would be plenty, and some listeners might even like 5 watt amps with your speakers.

Perhaps you can attend a show, not necessarily to scope out what to purchase, but to get a better idea of the kind of sound you hope to achieve.  That would help in any effort to improve the speaker you have,or guide you in finding better cables, in use of room treatments, etc.  There are no universally better parts; a change wrought by a particular choice might be going in the direction you want or it may go in the wrong direction.  But first, you need to be clear about what direction you want to take.  Cornwalls are lively sounding speakers whose vivid and exciting sound may come at the expense of sounding rough.  Are you looking for an even livelier sound, or are you willing to trade off some liveliness or detail or some other quality for something else, like a warmer sound, or deeper bass, smoother (less edgy) sound or whatever.  These tradeoffs and adjustments can be made with something as simple as adding or subtracting speaker stuffing, or changing internal wires, or changing crossover parts.  It is NOT the case that technically superior parts (tighter tolerance, better electrical behavior) necessarily improves the sound.  I know a builder who hunts down old, technically inferior resistors that others would say muddies the sound because they work in his designs and match the sound he is trying to achieve.

Regardless of what sound you are looking for, to me, the first modification of modern speakers to do is to add L-Pad controls to control driver output.  Such controls are essential for tuning the speakers to your room, your system and your personal taste.  It is madness to me that modern speakers builders think their chosen driver balance is ideal for all situations. 

L-Pad attenuators look like a potentiometer, but they are two potentiometers in one,  that will simultaneously increase resistance in one circuit while decreasing resistance in another.  When wired into the speaker crossover circuit, they allow the crossover to “see” a constant impedance.  This is necessary because a simple attenuator would cause the crossover frequency to change with changes in signal levels going to the driver.  There should be plenty of discussions of these devices on the web.

In the good old days, level controls were common but a lot of people misused them and then complained about the sound and created a lot of hassle for dealers.  I think that is why they fell out of favor.  But, anyone here seriously contemplating upgrades is certainly capable of using them correctly.  It is a matter of patient experimentation.  If you have a three-way speaker, you would have two L-Pads, one on each of the two more efficient drivers so that their level can be matched to the least efficient drivers (typically the woofer).  Given two controls and the overlap of sound from the drivers, adjustment can be complicated, but one’s patience will be rewarded.

No harm in just looking (yeah, right).  For speakers with a lively sound like Cornwalls, but a bit more refined sound, I suggest looking at Volti.  For speakers that can be used close to room boundaries, like the Cornwalls, I suggest looking at Audio Note speakers.  But, there are many great speakers out there and a major regional show is your best way to hear a decent selection.