There is a rule to investing in assets......whether it is coins, baseball cards, real estate, anything. If you buy the very best of the best, your investment will double, triple, or more. If you buy an inferior, sub-par asset your asset may go up in value, but usually only 10% or 30% or whatever but not 900%. Take a 1887 Morgan Dollar silver U.S. coin and look at the historical appreciation of the MS-55 coins......it won't touch MS-65 or MS-70's appreciation rate. Same is true with .com against the other extentions. If you want to make big money you really need to stick with .com and buy the very best .coms your money can buy. If you don't have the money to buy the best, than don't do it, unless you are happy with 20% returns, which is low for domain names..
That is a one way of looking at things. I have had 500%-1,000% returns on aftermarket purchased .coms but I have also turned down multiple offers that would have given me similar or higher returns on hand regged and aftermarket purchased .pros. I'll give you two examples, I regged Piano.pro on 21 October 2007 for $99, on 15 December 2007 I got a $1,500 offer which I turned down. That would have been a 1,615% return in 55 days. I bought Offshore.pro for $600 in December 2007 and turned down a $4,500 offer for it from a Czech company in November 2008.
If you hand regged top .coms in the mid to late 1990s then you have reached the pinnacle of domaining and there is no need to consider alternative extensions. If like alot of people, you didn't get into domaining until much later the .com aftermarket route isn't necessarily the biggest money spinner. Selling casino.anything for $1,000 may be easier than selling the 81 millionth domainer choice in .com for $1,000.
.com domainers try to shepherd new domainers to the .com aftermarket because that's how they make their money and get exits on their investments. If a newbie pays $10 to register casino.anything, that's one less customer for a .com domainer. The problem with the .com aftermarket is that it's massively overpriced. I'm always looking to buy .coms but I rarely see anything I consider good value, I buy perhaps 1 or 2 .coms per year.
There is no right or wrong answer about whether people should buy .coms on the aftermarket or register alternative extensions. It's like choosing between investing in blue chip stocks and startups. Startups offer bigger returns but are riskier. Easy money blinds people to risk. Top .com domainers don't like to acknowledge how precarious their wealth is. If Google decided to change its algorithm tomorrow so only relevant content and backlinks affected page rank and stripped out the favourable impact of years of continuous domain registration, .com values would be hit badly. PPC is already disappearing, there is bound to be less type in traffic in future as internet users get more savvy and search engines deliver more relevant results by analysing content.
A whole raft of new gTLD's is the biggest threat to the domain industry ever but again, according to some people on this thread, it isn't worth talking discussing. It will be fascinating to see whether big companies consider their own brands to be stronger than .com and use .microsoft and .ibm. Also, it will be interesting to see how search engines adjust their algorithms. If somebody types in "Microsoft" it surely makes sense to rank any domain ending .microsoft which is owned and run by microsoft first. OK, Microsoft rank top anyway for Microsoft but what if there was a software compant called Bingo or Poker, then things could get interesting.
I see new gTLDs as marking the beginning of the end for "it could mean" ccTLDs like .ws, .cc, and .im. Where only the keyword supports domain value, unlimited keyword availability and better keyword extension fit is going to be very damaging. .com will be less affected than other extensions because of its preeminence but the new wave of gTLD's will inevitably make it more acceptable to use alternative extensions and that will hit valuations.
If you invest in alternative extensions, you should stick to branding suffix extensions like .tv, .me and .pro where the keyword and extension fit, or established and partially developed alternative extensions like .info.
I disagree with the generalisations made about .pro in this thread, it actually produces some stunning domains like Golf.pro, Football.pro, and Poker.pro. Go to the US trademark database uspto.gov, click trademarks, select number 3) search TM database, click Structured Form Search, add Pro in as a search term, then select Non Punctuated Word Mark in the field, finally submit query. There are 15,341 trademarks incorporating the word Pro, that's more than the majority of alternative extensions added together. .pro has been very lightly regged because until September 2008 virtually nobody qualified to register them at the second level and it cost $99 to register by proxy, since then only professionally qualified people have been allowed to register. The upshot is that only 10% of registrars by volume offer them. You can hardly bundle it in with other alternative extensions that are freely available to register and offered by every registrar. It's not a like for like comparison.