I agree with you that if we do not talk about grails that nowadays are raising stellar prices vintage Longines are in general a bit underrated but in my opinion this due to the reputation that the brand has today, or better to the market position that it is occupying. Swatch group decided to place Longines in a lower price range than Omega (I think 1000-2500? I do not know modern Longines'models and their prices very well) so this strategy maybe made the brand loosing part of its reputation. As a result some of its vintage models are not enough appreciated.
Anyway your two Conquest are beautiful, my favourite is silver dial with the gold indexes. The case back is very charming with the Gold fish.
Best.