Should I recap my speakers? If so who can do it?

I did my speakers with caps from Erse. VHQ metalized film. http://www.erseaudio.com/Products/PulseX
Very reasonable and I could not be happier. Excellent sound.
No need to change resistors. I would however, remove the FASTON connectors and solder directly to the board. Ditto if FASTONs are used on the drivers.

I beg to differ on the sand cast resistors

It depends on the implementation. MRA resistors are wire wound and designed to minimize reactance at RF frequencies.

If the original design was tweaked to include the resistor reactance, changing them could make a difference. Whether that difference is perceived as better is totally subjective.

Capacitor upgrades from 'lytic and mylar to polypro trump resistor changes six ways to Sunday.

What works well in one design may not in another. There is no free lunch.

Age is a factor for electrolytic caps. Industry standard life is 15 years. Even if capacitance is still within spec, ESR is probably quite a bit higher than when new.

Polypropylene caps usually sound much better than electrolytic or mylar.

Replacing 20 year old mylars with modern polyprolylene can be a revelation.

Film and foil are preferred, but more costly. High quality Metalized film work very well and represent the best bang for the buck.

Be aware that capacitor 'reviews' seldom take into account contributing factors and are valid for that equipment only colored by the reviews predilections and prejudice. As always, Your Mileage Will Vary.

Since some capacitors require "hundreds of hours" of burn in, which in itself may be questioned, there will innumerable other changes in line voltage, RF, ambient temperature and pressure, user acuity, etc. so as to make the ratings quite possibly specious.

And just how is someone who barely knows which end of soldering iron to hold supposed to ascertain all the parameters which go into making a functional crossover?

For all but the most basic cookbook crossover, which has an extremely slim chance of being correct for the drivers, it takes sophisticated equipment, knowledge and experience to be successful.

Comments like the above are the reason there are so many egregiously awful designs extant. Designing a decent loudspeaker is many times more difficult than designing decent electronics.