But the fact is, certain things are/were intended for Israel alone, of which I could cite multiple examples. You could too, no doubt.
With regard to tithing, again, why doesn't our tithing system include bringing our agricultural surplus to a storehouse and having a party with it?
And also again, what tithing guidelines are we given in the NT? You see, the point is, the standard is now HIGHER than in the Old, just as with the rest of the law.
It's just like the sacrificial system - all it did was point to an ultimate fulfillment. The ultimate fulfillment of the tithing system is found in Jesus' instruction on keeping the law, which He made about the heart rather than the outward appearance.
We see that in the only times the NT mentions tithing, when Jesus is reprimanding the Pharisees.
Matthew 23:23-28, "Woe unto you, scribes and Pharisees, hypocrites! for ye pay tithe of mint and anise and cummin, and have omitted the weightier matters of the law, judgment, mercy, and faith: these ought ye to have done, and not to leave the other undone. Ye blind guides, which strain at a gnat, and swallow a camel. Woe unto you, scribes and Pharisees, hypocrites! for ye make clean the outside of the cup and of the platter, but within they are full of extortion and excess. Thou blind Pharisee, cleanse first that which is within the cup and platter, that the outside of them may be clean also. Woe unto you, scribes and Pharisees, hypocrites! for ye are like unto whited sepulchres, which indeed appear beautiful outward, but are within full of dead men's bones, and of all uncleanness. Even so ye also outwardly appear righteous unto men, but within ye are full of hypocrisy and iniquity."
We are called to give from the heart, which for most people probably means a greater sacrifice than just 10% of our income. We are called to give with sincerity, serve others with selflessness, because Jesus' point was that what goes on in the heart is far more serious than what we actually do outwardly. The same was reiterated by Paul.
A pastor friend of ours puts it like this - he says, "I don't give to get, I give to give." He considers it a privelege to bless others through giving, just as Paul said (and I paraphrase) - everyone as he feels in his heart, not begrudgingly or because he feels he has to, but because he wants to, because God loves a cheerful giver.
No one is suggesting that we shouldn't give, and give abundantly. But it's about the heart. In other words, giving because we feel we have to is a lot different than giving because we want to - the former is worthless in God's eyes. David lends some insight when he is repenting of his sin with Bathsheba -
Psalm 51:15-17, "O Lord, open thou my lips; and my mouth shall shew forth thy praise. For thou desirest not sacrifice; else would I give it: thou delightest not in burnt offering. The sacrifices of God are a broken spirit: a broken and a contrite heart, O God, thou wilt not despise."
To add to what you wrote, I believe the Holy Spirit will guide Christians in their giving, and help them to be good and sensible stewards of their money as well.