For me having used a surface pro first gen as a daily driver, the SP5 2017 has been a significant upgrade. Happy with the choice. I've considered waiting for usb C support, but can manage fine with the current specs. I don't think I would go for an upgrade to usb c if the opportunity came. It does allow a lot more freedom when mobile as usb c charging is more ubiquitous than the proprietary surface charging. But the latter is fast, the SP battery life is significantly better, that I don't really need to charge when at work for my daily use. Charging to full at home is within 2 hours, that's fast.
The achilles heel in my experience is that the proprietary charging. The brick is relatively big and the chargers are expensive. Lose it and its a daychore to find and get one the same day. With usb c would be far less worried, but I'm not sure if it'll charge as fast as as the surface charger. Compromises, compromises.
I will not upgrade for some time. I think these devices are too expensive and good to be replaced within 3 years. That's what I've experienced with the solid firstgen device. The surface pro, if used and handled properly can be used fine for at least 5 yeats in my experience, likely longer, the limiting factor is for microsoft to finish a half baked windows 10. The surface pro deserves a much higher quality stable better featured tablet experience and better performance than is currently being delivered.
For me the lack of joining a faster hardware upgrade cycle is really windows 10 lagging in quality for the surface line.
I would consider upgrading if these conditions are met:
-at least 50% better battery life in teal world perfirmance
-at least 40% better chip performance within the same formfactor
-a better built in application to hold the pen. The magnets are strong, but the magnets are still not good enough in many conditions to not loose the pen. Buying a new pen is an expensive affair you will not want to lose often.
-proprietary fast charging and data transfer over usb c
-a better camera with better image taking algorithm.
-built in gps