I highly encourage speaker building. It's really not that difficult and is very rewarding and yes, they can sound as good as any commercial units.
One area of DIY speakers that could use improvement is the cosmetic finish. Most of the DIY speakers look home made and not in a good way. Most I see are poorly done.
The world of veneers and stains and high gloss finishes requires very specilized tools and years of experience. These products are NOT available at Home Depot. You can get a decent appearence if you stay with basic finishes. However, you will NOT achieve the level of Sonus Faber high gloss finish. High gloss piano black requires a good deal of expertice.
It seems a shame to pay an auto body shop to paint speakers for the same as the entire cost of the kit, possibly more. It also seems a shame to have a new speaker end up looking like a high school project. Some do OK, but not many. It's a sore spot.