The income is created out of nothing
That is not entirely true. Income is - at least with this mod - generated when a player digs or places something for the first time each MT day. There is no money given if the player is not logged in or does not dig or place anything. So it is no more or less created out of nothing than anything else withhin the game.
The solution to this is a protector node, that protects a certain area (like this one but simpler) and needs money as fuel. The money it uses up just disappears and when it is used up the area becomes available to public again. But you are able to refill it any time.
Many ideas sound good at first but do not work out or are even harmful when applied. This way of protecting land has one major drawback: The income will be activity-based (players have to log in and dig/place something), while the land will get unowned after some fixed timespan. Players will have to log in and pointlessly dig/place nodes regulary just to maintain their property. Again, under rl circumstances, that's necessary for most types of property. But MT is not rl. It's a game people play in their spare time for fun.
Plus protection is not really the same as property. Protection mods exist as a defence against griefers who would otherwise pointlessly destroy other peoples buildings just because they can or steal material that looks intresting to them. Protection mods fascilitate the work of moderators because they don't have to constantly worry which building got griefed today and who needs to be rolled back. Protection mods help against players who do not follow the rules. The second - albeit minor - advantage of protection mods is that you can see more easily who built what.
To me, everyone needs to get as much land as the player can fill with halfway decent buildings. In the end, neither land, buildings (selling buildings is utterly pointless) nor materials (stored in a chest) have any real value. The only value lies in the fun you have while playing, and the fun visitors have while looking at the buildings and enjoying the sight.
That doesn't mean there can't be trade. Trade usually happens if someone has something someone else would like to have. It happens quite often that for a particular building one has in mind the own storage of the desired material turns out to be too short. That's when trade comes in.
On Redcrabs server, Mese and steel ingots act as some kind of "currency": If you don't need anything specific right now but have a potential customer, some Mese or steel can't hurt - it can be used for many purposes later on.
Servers that have technic installed are usually on an inofficial copper base (copper lumps/ingots = money) due to the high amounts of copper the technic machines require. This is mostly true for Vanessas survival server. Copper is required to generate new technic playthings, while for money...you won't get much (nobody sells much of any intrest for minegeld). So minegeld is kind of like the money in the DDR used to be - it exists, it's somehow money, but the really intresting things require hard cash. Plus minegeld pretty soon becomes unhandy (Stack of 5000 MG? And want to buy something for 100 MG? Good luck.). The barter tables of this mod are fine because they allow to trade combinations of goods. The disadvantage is that you have to store what you want to trade on each side - that binds money (needed as a price indicator) and the goods (the sample item can't be sold); you can't offer some goods in return for something you need and don't have yet.
The best solution to the money problem in my eyes is the one used on linuxgaming.us: You get 100 credits for a stack of cobble and can buy land close to spawn for incredibly high amounts of money. Plus there are admin shops selling items that are not available through normal gampelay (wool, dyes, shops, ...). Normal mining is a source of income, while getting land close to spawn (=easy/fast to reach) and some building materials is a one-time money sink. That balances each other out fine.
Then there's the landrush server, where new players are a source of income (ca. 10 gold ingots worth), and where further money can be obtained through converting gold and silver into money (kind of like an admin shop that buys them). The server has the advantage of a huge player base - which is very good for trade. The disadvantage is that most players have so much money they literally don't know anymore what to do with it. While on the other side, money is not really necessarry - you can obtain everything on your own.
There are at least two testing servers out there who have a diffrent mapgen - MG nore and Dan's Realtest - both of which do not generate ores in the usual way. MG nore creates veins of the usual ores (so you may easily end up with tons of mese but without enough coal and iron and totally without ore xyz that you're in need of), while the Realtest mapgen creates deposits of ores far apart from each other. The frequency and amount of ores was changed recently, but with the original distribution, the "you get everything everywhere if you just dig a bit" way of obtaining changed to "got some stacks of xyz - but nothing else" - which is excellent to encourage trade. At least if there are enough players. With too few of them or in singleplayer, it would simply lead to frustration.
And please don't worry about more money beeing around. That's ok - players explore the map, dig building material up, produce buildings - the server grows. Money helps to fascilitate the trade of building materials and may be fun on its own (i.e. when buying a pie or a bread). Making some materials more difficult to obtain can encourage trade. RL time based rents of land do not fit in here.