If the spike is turning brown go ahead and cut it at least down to beyond where there is any brown; if it keeps browning further then I'd cut the whole thing down to the bottom node. It shouldn't have any negative effect on the spikes that still have blooms. The fact the spike is turning brown means the plant doesn't have the energy to sustain that much growth right now anyway so by cutting the spike you're helping it to focus on the spikes with blooms (which is what it's trying to do). You can use scissors or gardening sheers. Make sure they are clean though, or they could spread disease (this is mostly applicable when using one tool to cut multiple plants). I usually just use whatever scissors I have nearby and my plants have never had a problem.
Also wow, what a great looking plant!