Go ahead if you think it's worth it.
It's true that Incubus/Spike is a powerful combination. Incubus is also difficult to enchant. At Rank 9 - having some 50+% success rates means you get about half a chance of the broadsword losing durability. A failure eats instantly into the durability. Rank A step enchant is also risky at 77% unless you are enchanting on Thursdays, which goes to 85% if I'm not mistaken. You'll still be losing a lot of money this way. If blacksmithing eats up money and time but saves you just that little bit, think of the other things you could have possibly done within that time to earn more.
Either way, it's going to take up a lot of time and/or money to get Incubus/Spike. Probably about 20 broadswords for one if you aren't too optimistic about your luck.
Also, if you are thinking of making a lot of them for profit, I really don't recommend it. You are better off selling tons of Stamps for profit, unless there is a huge demand for Spike. I don't know how it is over there, but people here keep telling me that buying one is too expensive, which is why they are risking it.
If you are just thinking of making a few sets for your own personal use (and not intending to do this for the long run), I don't see why you can't trouble the mentioned blacksmither for a little bit. I'm sure he will understand. Providing materials for him also means that he's getting some help with blacksmithing training, which I feel is a win-win situation for the both of you.
I rarely see people with Incubus Spike over here. Most of the people who enchant Spike with me just leave it as it is or enchant Wolf hunter as the prefix.