I enjoyed Spirit Tracks a lot when I was growing up. It was the Second LoZ game I ever played, and I will still pick it up and play it every now and then. A Lets Play might be good to watch, but the amount of time spent riding around on the spirit Train could bore you very quickly. Apart from the transportation, everything else is really good. The side quests will take up a lot of time, if the Lets Play you choose to watch decides to partake in them. The bosses are incredibly fun, and the items you get are pretty cool too. Watching someone play it doesn't fully make up for actually playing the game, but I understand what you mean. I still cant afford to play Skyward Sword yet...
Its ultimately up to you. If you watch it now and play it later I highly doubt that will spoil parts of the game. It follows a pretty basic Zelda formula. Ive played this one at least 6+ times, and Ive enjoyed every run through.
Hope this helps!