I've never seen a bonnie without the tweeters installed, so I've got a concern. If you add a tweeter, make sure that it is pre-wired, and that it'* wired directly to your 5.25" speaker. Also make sure the 5.25" speaker has a passive crossover on it (a couple can-shaped deals soldered to the back of it).
Also, if you're planning on adding aftermaket HU anytime soon, you'll blow the tweeters if you turn it up very much. So you may just want to go aftermarket speakers if you want better sound.
I considered installing components, but decided to install 3-ways, after listening to the systems and comparing prices (3-ways=money saved). I was able to get a pair of 90dB sensitivity, 45 watts RMS (180 peak), 3-ways sony'* off ebay new for 40 bucks, including shipping.
'95 SSEi, few electronic mods (and a stupid coupler)
HU (Sony MDX-CA680, European Ver; Sony 4x3-ways; 91, 93dB)
Yup, that'* ISU