TGOM's Three Tenets of Technology Trading:
(Based on a reversal of the old horse trader's saw about white feet on a horse)
"One white foot, buy him
Two white feet, try him
Three white feet, feed him to the crows"
1) Do you need it?
2) Can you afford it?
3) Can you make it profitable?
If a technology trade meets one of these criteria pass it by. If it meets two of the criteria then consider it. If it meets all three, then do it now. But if #1 makes the difference between victory or defeat then do it earlier.
And if you want to see smoke pour from my ears and flames from my Irish proboscis, then buy a monopoly tech and have no sucker standing by to relieve you of the burden.
And since we will be doing lots of our own full bore research I have another tactic which I apply: if you do not succeed in beating a rival to an important, valuable, monopoly technolgy, then go to F1, move both sliders to 0 and try to buy it, but only when there is some way to get back most of the investment. The seller will give some credit for what has been invested and you should be able to make some coin back when you sell it on.
Since I usually don't build wonders until ToE and Hoover's I tend to ignore the optional wonder building technologies, except for Literature and Navigation. Literature for the libraries and Naivigation for the maps. Printing Press can be good too as it tends to be ignored and will frequently have a monopoly value.
Since this game is heading for Space we want to work the era change as hard as we can. That will mean researching or acquiring lots of the optional MA and IA knowledge so there will be trade bait for the Scientific nations' free tech at the era change.