The tunnel is definitely useful in early game to earn money and, as you pointed out, the need to start loading up the board factory quickly. As Tomohiko pointed out, you can still get some free money from the demolition of the tunnel after you have finished making good use of it.
+1 wow, Sell the pre-set tunnel !? it is interesting strategy. imho, i use the tunnel and Lower decks, around 4 mins. Because the tunnel is usefull, i can sell it same price after i use the tunnel some mins. +Lower deck is very useful, it will be a good Hub to Tool and Chair at bottom-Left . last week, i got a good score 16:20 yayy., (it says World Record is 16:10 on 2020.Aug.2) ... i need 10 more seconds !
