I think the fact that a good few teams haven't been competitive over the past few years must be of detriment to the competitions credibility.
Once the Scotish club rugby ship is righted, and these teams become genuine contenders, then hopefully their crowds will expand (with the help of some better marketing) to give the competition more spead in interest / fan fare.
There seems to be some differing ideals of who should be considered the league champions between NH and SH supporters.
Down here (SANZAR) we are subjected to a finals series for every competition (Club Rugby), with the winner being the champion. Others appear to disagree and see the team at the top of the table, after the season finishes, as the champion.
As some of you have stated above, having something to play for is of great importance in maintaining interest in the competition right to the final game, and having numerous teams in contention at the end adds to the excitement (as can promotion/relegation).
Obviously promotion/relegation would not work with the current setup, but I believe that a play-offs series would add interest and focus to the season, as well as increased revenues.
A top 4 playoffs would be a good line to draw from a pool of 10 teams.
1 plays 4, 2 plays 3. With all games being played at the home of the top ranked team. So if you're the top team at the close of the season, well done to you, but you are not yet the champions. You will be rewarded by having home advantage for your semi-final (and final if you win the semi) giving you the best chance to take out the ***le. It also means, if you win, that you were the best team in both an extended basis (round-robin / Heineken Cup juggling play) and in 2 presure fuelled / knockout games (semis and final), thus becoming the undesputed Celtic champs.
The biggest incentive to be top of the table though, would be in the massive revenue generated from having two extra (hopefully sold out) home games.
Alternatively, if the fan support warranted it, the final could be moved to a national stadium (Murrayfield, Millenium, Croke/Landsdowne) to generate more revenue and help fill the national body's (IRFU, WRU, SRU) coffers and provide more money to plough back into the grass roots that drive the game forward.