if you're just riding for fun and commuting and for errands and what not, what do you care about weight? in my experience, weight is what racers should care about when they weigh 150 lbs. and need a bike that doesn't break and is similarly light.
keep in mind that i say this as someone who is probably about 215 right now: my bike is probably about 25 lbs. and i don't care a lick to make it lighter. there's just no need. i can lose any amount of weight that i'd like my bike to lose much more easily and cheaply.
and now for the advice portion: don't pay attention to the weight. if you want something that functions both as a flat and as a clipless, weight is a non-issue. go for what works for you. based on your description of your riding habits, my guess would be that the cheaper option is probably the better one, but it might be less durable, or less comfortable or have some other deal-breaker associated with it. chances are, though, you won't use it in a way that'll force you to notice.
my second caveat: i love grant petersen and his biking philosophy ( http://www.rivbike.com/article/misc/tips_for_happy_riding ).