SLi means more options for us consumers, that's FANTASTIC, not a bad thing.
The only thing that has drastically changed in the graphics industry is that companies are saving money by using more partially bad cores for lower end gpus than they has previously, which are drastically slower in certian circumstances.
With the Geforce2 series, you had the GTS/PRO/ULTRA that were all basically identical, just clocked differently. The sub $200 MX is the exception to this. People seem to think that you were able to buy a card for $150 and get $400 performance and that simply was not true at all.
Those people might have purchased the midrange card once it dropped to low end pricing (low end is $100-200), but these cards were introduced at least with an $199 retail MSRP. The Geforce2 GTS was $300-350 when it came out, I still have a PC Gamer that says that. It was easier to wait for prices to drop at that time because the software wasn't as demanding as it is now.
The Geforce2 Ti4200 was again introduced at $199, and because some people purchased it months after introduction and clocked it to ~4400/4600 speeds it is thought that todays cards must be able to do that.
The memory interface was universally 128-bit then (in the GF4 generation) which basically set the stage for it to be assumed every generation must have unified bandwith architecture. It was great at the time, but those days are over folks. Even the 64mb Radeon 8500 came out for around $300, and it was ATi's only offering outside of the LE which was $250ish for a while, I don't know the MSRP)
As far as I'm concerned the $100-200 market has been (for the past 3+ years) and always will be garbage, cut down, graphics. You go up another hundred bucks and you have something worthwhile.
With SLi you get performance now. If someone has the money to spend it is foolish to recommend against it, if their main focus is gaming. Personally I can't wait for ATi's implementation of SLI, an after having bad experiences with my 6800 cards I will probably switch back over to ATi, but nVidia does have a very good technology that not only is great for marketing, but it puts out fantastic performance in games that we play NOW.
Personally I wish there wasn't such a large disparity between the high end and low end parts so that software guys could create great performing things for everyone, but that isn't going to happen.
Just my 2 cents