I get it if you're trying to use a cross shaped D-pad, but as stated by others, a Sega circular D-pad takes little time to adjust to. Even with Emulation and PC gaming, I use Sega style D-pads(what can I say? I personally prefer face buttons to shoulders. Though the one I use has those as well, so...).
The controls certainly wouldn't have hampered the games sales one bit, as like I said, it takes little time to adjust to with the consoles actual D-pad. If anything hurt its sales, it'd be lack of name recognition(not sure if Shining would have helped or not at the time), and the fact that it was an adventure game on a console thats install base were typically more sports/action/arcade oriented. Even Zelda at the time was lucky if you could say it sold to about 10% of the consoles owners, nevermind something that didn't have a predecessor on a massively successful predecessor of a console that held 90% of the market.
Shadows wouldn't help one bit. You wouldn't see where it is over a gap, for starters. What would is a sort of... I don't know how to describe it, but like an arrow or something that highlights the squares directly in front of Nigel for upwards of 4-6 spaces(however far he ever has to jump across at any point in the game).