I have added several accessories to my Pace 500 and I ride every other day for exercise.
My list is as follows:
1. Brooks B67 Upright Saddle: (It is much cheaper on Amazon and I got it in 2 days from a local vendor)
Brooks B67 - It took me about 300 miles to break it in, but it has completely eliminated any soreness when riding 30+ miles at an average speed of 20 MPH.
2. Redshift Sports Suspension Seat Post: (I bought it from Redshift as they had a 15% discount coupon at the time)
Redshift Suspension Seat Post - The seat post is more expensive than others, but is far superior with its design and simplicity. I set mine to my weight and it has been a perfect compliment for our hard tailed bikes. Small and medium size bumps disappear and large bumps are greatly minimized.
3. Shimano Deore XT PD-T8000 SPD Pedals (I bought on Amazon)
Shimano Deore XT - These are two sided pedals, so I can also use them as normal pedals when riding leisurely on the weekend with my wife. The clips on the bottom of my shoes lock my feet into place so they are not sliding around when going over uneven surfaces. I am using the Shimano SH56 Multi Directional Release SPD Cleat which makes it very easy to rotate out of when needed.
Shimano SH56 Cleat
4. Hafny Handlebar Bike Mirror (Amazon)
Hafny Mirror - This mirror is mounted on the left next to the throttle which gives it plenty of length to see around my arm.
5. Light and Motion Urban 500 & Vya Commuter Combo (Amazon)
Light and Motion Bike Light Combo - Good lights for making me more visible on the front and rear while riding on the road.
6. Roam Universal Bike Phone Mount (Amazon)
Roam Universal Phone Mount - Holds my iPhone 10 XS securely when riding.
7. Kenda Kwick Drumlin Tires in 27.5" x 2.2" (Kenda Online Store had a 15% discount coupon - Search for them online)
Kenda Kwick Drumlin - They have a higher rating in all 4 categories (Speed, Grip, Protection and Durability) than the OEM Kwick Seven.5 Tires and they are cheaper. I have not installed them yet, as I am waiting on a replacement spoke for the rear wheel.