I think that you may have missed my point. I also don't mind that World Wonders exist. What I mind is that many of the Wonders currently in the game are things that anyone would copy if they really gave the benefits associated with the wonder. A mill which is very efficient at processing food and materials? Of course I will copy it. A vault to keep my gold in, which also gives me income based on my total wealth? I'll copy that, too. A tower that acts as an air shard? Only if I 1) have an air mage of some level, 2) have or am likely to have good air spells (i.e., I'm not focusing that air mage as a fighter or governor, but rather as a spell caster), and 3) actually need more air shards.
If you'll notice, most 'wonders' in the real world are things that are either neat to look at or took a lot of effort to build. Most of them serve little or no functional purpose, so there is little motivation to copy it. Any that do serve a purpose are either hard to copy because they need certain geographic features to work (i.e., very large dams or canals) or have aspects related to their construction which are closely guarded secrets (i.e., certain types of machinery, although that usually gets stolen/copied/reinvented/made obsolete within 100 years of development), or are very expensive (i.e., certain types of research lab such as the Large Hadron Collider, International Space Station, etc).
I agree that the mechanic of 'holding' on to a wonder by keeping it in the build queue should be revised - I see no reason why the fact that I'm building something should keep someone else from trying to build the same thing (unless, of course, we add a "Stop building that or I will invade!" diplomacy option). I just disagree with making Wonders out of things that everyone should be able to make. Wonders which give a city +5 happiness or grant some faction prestige or generate some influence each turn or act as a shard of some type or another are fine with me - these are the more abstract resources in the game and are things which I don't necessarily see as something that would be worth the effort of copying. A treasure vault that increases my treasury by 1% per turn? That is worth the effort to copy, because 1% of my treasury can be equivalent to the income of several cities, depending on my choices in developing my nation and how much of a treasury I actually have. A mill that makes everything in the city produce more efficiently? I'll copy that since I always want my factory city to spit out troops/buildings as fast as possible. A tower that gives me 1 prestige and an air shard, and takes 30 turns to build in my highest production city? I'll pass, there are usually easier ways to gain prestige and air shards, and by the time there aren't I don't really need the benefits anyways.
The biggest problem I have with the current wonders is that they are not things that are 'nice to have, but I don't really need them', they are things that are significantly better than anything else I can come up with for the rest of the game. +25% food and production to a city off of a second tier technology? There isn't anything else in the game that can match that for a single city. Increase your income by 1% of your treasury? I've had games where that is the only reason my income is positive. To make this one worse, though - it probably goes to the person who has the largest empire since they have the most cities and thus produce the most research, which means that they more rapidly finish the resources, and since they invested in researching out to Economics in the Civilization tree they probably also have the highest base income, and thus need the extra money least. If Economics made it so that you gained 1% interest on your treasury and the Treasury Vault added another 1%, I would be less bothered, but still very confused as to why only one person in the world can built a vault in which to keep money.
Essentially the current Wonders of the World are mostly bonus buildings that provide a benefit that anyone would like to take. There isn't any real reason why, having the same technology as the group that build one of the Wonders, I would not attempt to build one. If on the other hand there was an actual downside to the wonders (that Great Mill, it processes the food and materials really well, but everyone in the city is fat, lazy, and hates doing research, plus it costs a King's ransom to keep the thing running!) there would be a legitimate reason for me to consider not building one or copying the existing structure. This is in some ways the case with Ereog's Tower - I get an air shard and some prestige, but if I don't really need an air shard then I'm not that interested in occupying my city's build queue for 50 turns building it, and I'm not going to rush-build one to avoid the production time because it costs an arm and a leg. Moreover, one or two prestige probably doesn't matter to me by the time I can build Ereog's Tower, so that benefit I don't mind missing out on. The Merchantcross Bazaar I can understand from the perspective of "well, there aren't that many merchants willing to risk wandering the wilds, and they've already found a good place to sell their wares, so building one myself won't do me any good."
Wonders which grant small bonuses to prestige (for the time in the game that you can get the wonder), or which act like a shard or two, or which grant a growth bonus in a city - these are the types of wonder that I can justify why I might not bother copying them. A wonder which acts like a great factory? Unless it meant a war I'm not willing or able to fight, I'm certainly going to try to copy it. And overt wars over the theft of technology are relatively rare, so I would be justified in not expecting a military backlash for copying it. Losing a bit of my standing with the original builder would be normal, but a war involving armies? Not that likely.