Eh, not true. I think that, as the series went on, we found that more affected Spike than he originally let on - especially once he realized he was in love with Buffy and became more prominent in the series and with the Scooby-gang. Spike was funny and none too serious on many occasion, no doubt, but he was also very...deep and the things he'd seen and done gave him more layers than anyone else on the show - including Angel, in my opinion.
In my humble estimation, I believe Angel was the one who never really showed emotion or exactly how things affected him. He was so very stoic about everything, even when Buffy told him that Spike was right and they could never be friends. (The episode where Spike kidnapped Willow and Xander in hopes of getting Dru back, I believe it was.)
Spike was very much an open book from...late season 5/early season 6 on. His facial expressions told exactly what he was feeling and his jokes, which before had seemed to simply be the dry humor of an uncaring and remorseless vampire, turned into something infinitely darker and became sort of a...defense against his open love for Buffy - something he begrudgingly couldn't hide from anyone it seemed.
I just found Spike to be a better character all-around but this is all just my perception.
