Evil has full text objects support and ci( works for me though I use Emacs+Evil and not spacemacs.

You'll want to add "evil-surround" for dat

I found little or no disfluencies in the keybindings/text objects etc and I use them extensively. Though you'll want to add some of the core emacs keys to your repertoire as many of them have no natural vim alternative.

evil-surround is not necessary for dat, that is present in core evil.

'ci(' works, I just tried it. I don't know the 't' parameter there, but 'da(' works as expected as well.

Strange, I just restarted spacemacs and now 'ci(' works. In the previous session I've changed some settings and that seems to have irritated spacemacs.

't' is for html tags so pressing 'cit' anywhere on '<width>280</width>' will do what you're expecting. :)

I only just noticed this now, but `dit` and `cit` only works in html (and other web derived modes) in spacemacs. I guess some of the stuff only gets set up on the major modes.

The "t" text object should work in all modes, if it isn't working for you then there's something going wrong.

Every text object I've tried has worked great for me (even non-standard ones like cia/caa from arg-text-objects)