worn tie rods will definitely make the steering wheel feel loose. so will bad ball joints too though, and make sure the wheel bearings are good also.
you should absolutely replace worn out suspension parts, because your wheels will fall off and you will have a bad wreck if you ignore it.
you should also definitely get an alignment when tie rods, or any suspension piece is replaced. you have no idea what the setting were when you started, and you have no idea what they are when you are done. unless you enjoy buying tires. quick example: i was aligning my crx, L outer tie rod end was bad. with the alignment heads on, toe was at -.17 degrees. 19 turns off, 19 turns back on (even left the jam nut in place) put the head back on, recalibrated, left toe was now negative .26. so just because you count turns, doesnt mean its perfect. it doesnt take much to make a change.
And about the loose steering at 70. that is most likely your tires. soft sidewall, low airpressures, theyll make the car seem floaty and unresponsive at speed