Danswifey, congratulations on your Sebo D4 purchase! I hope you enjoy it for many years. It wouldn't have been my personal choice....I personally would have gone for the Riccar Prima or Aerus Platinum. The Sebo is nice, but I find the lack of features it has on a canister in it's price range is unacceptable. For instance, the powerhead on/off switch should be on the Hose Handle, not on the powerhead. There should also be a headlight on the powerhead & a quick release pedal, not have to stoop down to release.
Regarding your two Riccar uprights....if I was you, I would take your cleaners in to have them serviced & get them performing optimally again. You have two very good vacuums, in my opinion, that should last you many more years & along with your Sebo make a good house-cleaning team. I tried a Simplicity Freedom back a couple of months ago, & was blown away by the power it has....amazing for a 8 lb upright! There is a cordless version of it to be released soon, & I am very tempted to buy it.
Best of luck with your Sebo....
Rob