There is a lot of commentary mixed in with your question(s), so I will do the best I can. Having worked on Pulse furnaces both first (G14) and second (G21) generation, I should be able to offer up some observations and recommendations. You are correct in that the Pulse furnace was quite unique and as you have stated from your own experience customers are not happy with the prospect with having to replace it with a more 'conventional' unit, although they are quite efficient themselves.
If I were in your situation, I would be taking the following into consideration in making my decision.
#1. what is the professional opinion that has been given regarding the furnace? You reference a laundry list of components however you state that the furnace is running, albeit temporarily?
#2. you state that you have the system under a maintenance program so there should be a level of trust between you and your service provider. If that is in fact the case, there is no reason for you to question his observations and recommendations.
#3. if you are not the original owner, the furnace is outside of the heat exchanger warranty, pressure issues aside.
#4. if you plan to be in the house for any length of time whatsoever, I would go ahead and plan to invest in a new furnace. You would be far better off to do this than to invest in the replacement components you listed.
#5. the efficiencies and design of new units provide you with an even higher level of efficiency than what was associated with the Pulse. (I'm speaking of Lennox).
#6. I would recommend upgrading the furnace, and then when the time comes, changing out the air conditioning portion of the system with a heat pump for a dual-fuel configuration, maximizing your efficiency.
#7. I know it is tough to do (I had a G14 in my home, that was a working, display model) and loved it. I actually had potential Pulse purchasers come to my home and listen to the operation to be sure they were comfortable with the 'sound.' Although different, no one found it to be objectionable.
Time to let go. Invest in a new unit. Make a methodical decision on YOUR terms, rather than when the furnace shuts off and your decision is driven by panic and temperature.
Good luck.
Irish