Crossover 101 Nebie Dalquist DQ-10 Help

I just found a pair of Dalquist DQ-10 and just love the sound.  I have an NHT 8" sub with external amp to supplement (not connected yet) the low end.  I actually have two pair (one newer with yellow capacitors (mirrored) and the older version with the blue not mirrored)). So far they sound great but read too much about the DQ 10 crossover and a little confused: 
1)  If the capacitors read the correct microfarad am I OK or is there a reason to upgrade?
2)  If the capacitors are good or week, should I upgrade to newer on board crossover that I saw on the bay?
3)  If my capacitors are good or week, what does the external crossover DQ-LP1 do and what is it's advantage over the original?
            a)   Does it bypass my on board capacitors or even use my original capacitor/crossover?
            b)   Do I even need the on board crossover if I have the external  DQ-LP1 or do they work together?
4)  Can anyone tell my why people replace the small tweeter and what would be a great planar replacement?

I plan on keeping these and don't mind putting a little work and money into them, plus my wife think they are beautiful and gave me the OK to purchase!

Thanks in advance
I'm not familiar with the DQ-10, but the DQ-LP1 is specifically and solely for adding a subwoofer to any loudspeaker. Any x/o included as part of the loudspeaker itself is to provide filtering for it's integral drivers, not for adding a sub as is the DQ-LP1.
If the caps of your DQ-10s are the originals and yellow, they are metalized Mylar and will still work well. There are numerous, more modern, film caps, that(if matched for values), will improve your sound quality, over these older Mylars. If the blue ones mentioned are original, they are aluminum electrolytics, now over thirty years old, and will need replacement, though the system will still(in all probability) function . Something that may(arguably) be the weakest point of the system’s design, is the Motorola piezo supertweeter, that Dahlquist used. I always replaced these with the ribbon, that JVC was manufacturing, back in the day. If you upgrade to a new ribbon, it will need it’s own high-pass filter/attenuator, as the old one was designed for the piezo, which(electrically) looks like a .15uF capacitor, in series with a 15 Ohm resistor. Ragnar, which is comprised of some of the old Dahlquist crew, offers upgrade kits, for the DQ-10: As mentioned: the DQ-LP1 was designed to integrate a powered subwoofer, in an actively bi-amped system, and has no other function. Some(currently available) ribbons: