There is no "right" or "wrong" on this. Like I wrote about here, it's all about being honest with what works for you. But in this case I do believe there is a happy medium. It's called "presenting options." If you gather your child's input (what colors they like, patterns that make them happy, what kinds of activities they most want to do in their rooms), and then present them with choices that meet their needs and your own, everyone wins.
My two girls have shared a room for as long as they can remember. Lately my 5 year old has been struggling with bedtime and keeps my 7 year old awake, so we are considering moving the older one to the guest room in the hopes of creating smoother nighttime routines. The room is "finished," and while it is colorful enough for a kid, it is a bit grown up, and it seems wrong to move her in there without making any changes. While I do not want to spend much money in there, I would want it to feel a bit more like "her" room.
There are some parameters, naturally. I would not like to paint, though of course that would be the lowest-cost way to make a big change in the room. The furnishings and new bedding would stay. So, I like the idea of swapping out some of the textiles and/ or art (currently this, this and this) to make the space more fit for a going-on-8-year old.
I've been playing around with the idea so that, if we decide to move her, I'll be ready to talk through her input and present some choices.
I like the idea of connecting to the orange in the girls' existing room down the hall. These two schemes would swap out rugs and pillows and use some extra white Ritva curtains panels with tassel trim added like I did here (scroll down).
These two actually get MORE colorful and push the eclectic bohemian feel even farther.
But, knowing my daughter, who will only ever wear monochromtic outfits, I have a feeling we would hone in on the blue and white palette and keep things very focused with either the existing red (curtains), or a focus on yellow (from the wood tone of the desk in there).
This last one feels most like her. It is fairly monochromatic, she adores stripes, and the girl on that pillow has glasses just like hers.
While I actually hope we can keep her where she is, I look forward to transforming the space together eventually (even though my 5 year old will want equal treatment in her room.)
Is't it amazing how much you can change the vibe of the room by changing just the textiles?