There is no Apple Smart Keyboard for the Mini 5 but it can be used with Bluetooth keyboards.
As for whether it is worth more, I guess that’s a question that’s best answered by weighing up the specs. The Mini 5 has more RAM, at 3GB as the 9.7” Pro was only had 2GB (half that of the other Pro models, the exception being the 1TB 3rd Gens.) The Mini 5 also has a processor that is 3 generations newer, albeit the Pro uses an X variant and the Mini does not. Camera wise the Mini is has 7MP on the front vs 5MP on the Pro, but the Pro is better on the rear with 12MP vs 8MP on the Mini. The quad speakers are unique to the Pro models.
The 9.7 Pro WiFi is priced at £399 refurbished, for 32GB storage. The base Mini 5 is £399 for 64GB. So, price wise, Apple seem to consider the Pro as being worth more (half the storage and refurbed for the same price, the original price being listed as £519.) Incidentally the £519 given for the 32GB 9.7” WiFi Pro is the same price as the 64GB Mini 5 Cellular.
The 9.7” Pro is the next lightest device after the Mini, lighter than the 2018 iPad which benchmark wise isn’t far ahead of your Pro and lacks other features that your Pro has (quad speakers, better cameras, laminated display, True Tone.) Are you wanting to either keep/return the Mini and sell/keep the Pro, or might having both be useful to you? The Pro could be used for keyboard work or when you want a larger screen for watching videos on, with the Mini useful when you want a lighter device. The Mini 5 is bound to receive iOS updates for longer if you don’t plan on getting another device for some time. At the moment it is unclear whether Apple plans to keep the 9.7” size around (Air 3 went to 10.5” and the 2018 iPad has the A10, a 2 and a half year old chip.) The Mini might be the only option going forward for those not wanting anything bigger.