I'd take the cost of the panniers out of your consideration since that would be a purchase no matter what you do.

That leaves, tires, saddle, and pedals. Realistically if you buy another bike, you are probably looking at buying saddle and pedals anyway. Most bikes don't come with pedals anymore and most of us swap out the saddle before all is said and done.

That leaves tires.

Honestly I try this bike out if you love riding it anyway. All the purchases you are talking about are ones you would probably end up making even with a new bike. Then if you decide to go with another bike, the accessories are already there.