Bogota is not as bad as people make out!!!
There is plenty to do for 4 days here. Some travelers stay 1 day and then say there is nothing to do here! The nightlife is great in the Zona Rosa area and in Chia, so maybe worth planning your time in Bogota over a weekend. The bike tour and/or graffiti tour are meant to be good. The salt cathedral is a day trip in itself. 60-90 minutes to get there depending on where you are staying, with a free 2 hour tour inside. So allow a minimum of 5 hours. Climb Cerro De Monserrate. Visit the museums.
Insider Tip:You can get to the Salt Cathedral very cheaply (2,000 COP by Transmilenio to Portal Del Norte, and then a bus to Zipaquira, 4,800 COP; so only 6,800 COP to get there). The cost to enter the Cathedral is 25,000 COP, and you get a free 2 hour tour inside.