Nightlife is great in Nairobi, and the weather is a little chillier in the winter (good for someone not used to living all year round in 29 degrees Celsius).
Uber gets you anywhere for $2-4 and in all of Africa, the drivers were less likely in Nairobi to ask to cancel and get cash for the ride.
If you like animals, I highly suggest a safari in Nairobi National Park. You can hire a driver for about $100 for 4 hours, and this is suuuper affordable compared to other safaris.
The SGR railway gets you to Mombasa in about 6-7 hours for around $25 in first class if you need some beach time.