Bearmaster, I think it is very common in the Church today to undervalue the Old Testament much more than the New. All the same you have highlighted some very precious passages that wonderfully remind us of the grace that is ours in Christ.
To add to your verses I would also include the following which show the value also of the Old Testament and God's law in particular,
Rom. 9.31-32: "But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness. Wherefore? [Because they tried to keep the law? On the contrary...] Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone... (see also Rom. 10.3)
Notice that in the OT when they tried to follow the law as a covenant of works they stumbled at the stumbling stone. Those like Abraham who believed on the comming Messiah were counted righteous through faith alone. In other words, the covenant of grace is not new to the New Testament.
Rom. 3.31: "Do we then make void the law though faith? God forbid: yea, we establish the law."
1 Tim. 1.8: "But we know that the law is good, if a man use it lawfully."
James 2.10: "For whosoever shall keep the whole law, and yet offend in onee point, he iis guilty of all."
1 John 2.3-4: "And hereby we do know that we know him, if we keep his commandments. He that saith, I know him, and keepeth not his commandments, is a liar, and the truth is not in him."
1 John 3.4: "Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law."
John 14.15: "If ye love me, keep my commandments."
Matthew 5.19: "Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven."