everything the OP said would happen, but to a lesser extent than he says. Bots would still be rampant in highsec, and there would still be huge numbers of carebear noobs who don't know how to play the game.

If highsec income were cut hugely at the highest points, say 75% less income from incursion vanguards in highsec and 50% less incoming DPS, no more incursions other than vanguards in highsec, no more level 4 missions in highsec, the top anomalies give 50% less income in highsec -- and if resource generation were reduced greatly, say 50% less PI yield in highsec, no plasma planets in highsec, no ores above omber and kernite in highsec and those only available in small quantities in grav sites you have to scan down, and 33% less tritanium and pyerite from veldspar and scordite which would be the only ores available in large quantities in asteroid belts in highsec...

then people would get by easily in highsec still. Many would seek the greater fortunes to be had outside of highsec as well as the greater challenges to be had out there. But there would still be plenty of people content to bask in what highsec still has to offer: that is enough ISK to pay for the cruisers and battlecruisers they use to run level 3 missions, enough ISK to pay for the mining barges they use to mine veldspar and scordite, enough ISK to pay for the ships they use to run the nerfed incursion vanguards, and more ISK from PI sales than the cost of exporting the goods. In short, highsec living will still be viable, therefore people will still do it.