Going into an alternative grid takes an adventurous attitude and the creative desires to make something better. SL is by far the largest virtual world out there, that is obvious. However, the prices for sims in SL are extremely high, and with the world economy as it is, money should matter to some. Are the worlds like Virtual Highway up to par with SL? In some areas, no. In others yes. And in still others, they offer things you can't get in SL. The largest drawback is people not supporting the expansion of these alternatives. If they are all satisfied with the performance and service of SL, and think the prices of sims are just fine, then they will stay there and support the Lindens. If they feel $295 USD is a bit much to pay for a sim, they will look elsewhere. However, it is the large content creators who control the success or failure of a grid. As long as they refuse to take their products and creations outside of SL, they are helping SL to maintain their control of the industry.
As far as crashing and outages, I experience them more in SL than in Virtual Highway. Is it due to the small numbers? Possibly. However, it is also due to the size and power of servers, and the load on each of those servers. It does make a difference. Also, the personal interest shown by the owners of a grid affects how you feel if you do have a problem.
The new alternatives are there. And, for the age of them are far advanced from where SL was at their age. And, the prices make them even more desirable.