In regards to trendlines and wicks, I think there are varying...

In regards to trendlines and wicks, I think there are varying circumstances where they can be a bit sketchy or very important. I've found a few examples here that might be a bit interesting.

In all the white lines there is a lot of wiggle room with them. Obviously the left side of the line would remain where it is but you could grab the right side and move it up or down a little bit and it would look to still be obeying the initial trend but might give you a very different price range the further you get to the right.
Example 1 would have given you a rough idea of a support zone for the downtrend after the high but there was a small wick that breached it slightly, you might have put your trendline on the tip of the wick but that would have thrown off the support and resistance points that happened shortly after by quite a bit
Example 2 shows a perfect support zone for the recent bounce off the bottom but being so far away it could give you a range of about 1.5c without disturbing the initial part of the trend
Example 3 there might have been several times where you would have adjusted the line to touch the wicks a bit better, after the price broke through it you might abandon it all together but it later started obeying the line as the downtrend resumed, again lots of wiggle room

Red line is useless, you would not have been able to plot any of it until after the fact and the angle is too steep to use as a possible support zone later but it is the sort of thing I would normally take notice of...
The blue line however is much more interesting and a good example of when I think wicks become very important. The line could only be plotted on the last arrow off the 15c spike, the two large arrows happened on very obvious spikes and was when I plotted this line, I ran the line back further and found another candle to support this. The two large arrow points were far enough apart to take out that wiggle room that was there in the other examples and has proven to be a strong resistance point also has formed the top of the flag pattern.

I do like to see trendlines supported by other technical indicators and line 1 is a good example of this. The 200sma and the horizontal support zone intersected all at the same point. Horizontal lines can be very helpful in those cases.

I would continue to watch lines like this one because now there has been enough points of contact to make it well set in its place and could later prove to be support or resistance especially it it lines up with other indicators