I decided to use a stratagy much like hockey refs use to break up fights in regards to this thread. (Let everyone wear out from throwing punches, then wade in

)
OK....My $.02 worth. Smoke is from worn rings/beat up ring lands from long term use and ether starting. That causes loss of compression, leads to poor starting. More ether needed to overcome poor starting. The problem snowballs.
I owned a gas 3000 for 35 years. Then I got a diesel 3000 to replace the gasser. The diesel was sold new in central Indiana. It DID NOT have engine pre-heater from factory. It cold started better than the gasser ever did, even with 35+ years, 4000+ hours on the clock. It had excellent compression and by original owners account, had never seen ether. (Some of us will not use the stuff. It's the equivilent of meth to a diesel engine IMHO)
If you'll be cold starting the engine frequently, a block heater is a good idea for a litany of reasons. Some diesels NEED them. Some can get by without. Manifold pre-heaters are a good thing on certain engines IF they help. Ether is bad. Ether is bad. Keep repeating that. Ether is bad.
Problems with CONTINUED use of an engine that's seen ether abuse; You CAN band-aide fix the problem by adding a heater to ease starting. Done early in the engines life, we wouldn't be having this conversation. It would have been a preventative measure then. Now it's a band aide. You CAN continue to run a worn engine. But there's a down side. Worn rings and worn out ring lands will wear cylinder walls MUCH faster than they should. Piston clearance adds up fast. That can (and will) lead to piston failure at some point. Then you have a door stop that was once an engine. I've seen diesels with 15,000 hours that still run. They might not implode, but they are a nuisance to start, waste fuel and oil, and are unpleasant to operate (smoke...) The ultimate solution would be to re-ring it as soon as is practical. You MIGHT save the engine with a small (relative to total engine replacement) investment now. It MIGHT need pistons too. (if ring lands are worn beyond service limits)
What I'd do; I buy tractors for one of TWO reasons. To use or to sell for profit. If I buy to use, I generally try to find ones that are in good condition and don't need costly repairs. If I buy to sell, the LAST thing I want to do is invest MORE money that I have to. That said, I've got burned a time or two and ended up with worn out engines. In those cases, I pull 'em down, check wear (rings, pistons, cylinder bore, bearings, cam, ect) Then replace what needs to be replaced. Next step is to recognize any possible reasons why they wore out prematurely. (ie cavatation/electraulysis, ether, poor maintenance, EXCESSIVE COLD STARTING, ect) and rectify that situation. If that means installing a block heater, then that's the next course of action. But if I plan on USING the tractor, or representing it as a tractor capable of being used when I try to sell it, I'd ALWAYS want the problem fixed and NOT just put a tourniquet on to stop the severe bleeding.
Your results may vary. I just like to fix things right so I can end up with a dependable tractor.