Hi Joe,
I am not an expert it this either but who is? I have a mix of engines like you but mine vary in age. I have an old Arnold Rapido Pacific that I bought for $17.00 in 1972. It has been in a storage box for years. I just pulled it out to try on my new layout to see if it worked. It did. A little noisy but it ran. I have also purchased 2 Kato "Mikes" and the Bachmann 2-8-0. All 3 of those engines run well on level track but the Mikes spin on my 2.5% grades with more that 6 M-T freight cars. I have ordered the traction wheel set for both of them to increase pulling power. So far the only engine that I have purchased that gave me any trouble was a Bachmann non-Spectrum 2-8-0 that quit running after 1 lap around my layour. Sent it back to B'mann and they returned it repaired, restored or replaced. It runs like a champ now.
That being said I think that the quality of the locomotives on the market today (especially steam) is quite good IF you stick with the Bachmann Spectrums, the Kato's and possibly the new Model Power Pacific (although I have no experience with it). If you have an opportunity go to a train show event in your area or visit with model railroad club to see what they run. GATS and Greenburg trainshows are great places to see the new products and to talk with other hobbist about a variety of issues including quality.
And continue to question and learn from the good folks on the Gauge. I have found them to be very knowledgable, helpful and a great bunch of people to know.