Hi- I have 2 full size Neff ovens installed “under the counter” below my induction hob. One is the top of the line “full steam” oven, one is their mid-range “regular” oven. Both have the slide and hide door. The regular oven is my daily workhorse, and I use the second steamer oven a few times a month plus extensively for holidays/ parties/ etc.
You’ve already justified the second oven needed question, so I’ll just focus on the steam aspect. (But I feel the need to clarify most steam ovens also work perfectly well as “dry” regular ovens too.)
I would say yes, it’s definitely worth it. The “full steam” function does some truly amazing things, like make a “no-stir” risotto in 20 minutes, cook sous-vide, and reheats things beautifully (terrific for pasta). The “partial steam” makes a noticeable difference for roasting meats in terms of speed and juiciness.
Besides the fact a steam oven costs more, the main downside of using steam is the cleanup, which is sweeping out/ soaking up any water from the oven floor and then leaving the door open for a bit to fully dry.