Would the focus groups also be virtual?
I can answer your question from a UX research perspective rather than a specifically community one, but the premise is the same.
The obvious advantage of focus groups is that they are more economical.
Less obvious is the benefit that you touch on – group interaction between members can encourage people to have ideas or connect to concepts through the group discussions that may not have made during an individual interview.
Another advantage of a group situation (which may be less effective in a virtual setup) is that people may respond very differently to a topic, creating a group dynamic which you can observe and glean further info from. e.g. If you mention a feature that is polarising, in an individual interview someone may not raise their concerns, or they may gloss over them. If the group debates the feature you will likely see stronger/amplified reactions. They may also interact non-verbally with each other (laugh/murmur encouragement/scoff etc).