I think that this is up to the definition of "publicly visible". If I have one upstream and several peers, that is to me "public". I see few (no?) other real reasons for assigning an AS that is not seen through two or more paths in the global routing table.

It is not that rare. For example we do have some universities which have one upstream (us, ACOnet) and peerings with other ISPs (for whatever reason) _but no transit_ from them. Some of them would be "visible" (e.g. those with legacy class B space), others would be proxy aggregated into our /15 and "disappear". But, to come back to another comment: we're discussing details of routing configuration (because that's "easy"?) but I haven't seen any comment yet on my question on price/effort vs. (expected) result ratio (maybe because it's a bit more difficult? ;-). Wilfried.