Lets crunch some numbers
In simple terms, you can work out exactly how much a lead is worth to your business. Once you have made this calculation, you need to consider how much you are currently spending to promote your (current) website.
Next, you need to consider how many more leads you think a new website will bring in (if your current marketing spend remains the same). A simple calculation can then be performed, and you can establish how long a new website will take to pay for itself.
For example if you spend $1000/month promoting your new website, which brings in $5000/month worth of leads, a website with a 30% higher conversion rate would bring in $6500 worth of lead value (with $1000/month marketing spend).
If your new website cost $6000 to have built, it would then take 4 months to effectively, provide a positive, relative ROI.
Once you start viewing a website as an investment (it is a sound one at that), you can really start to crunch the numbers and decide what is best for your business.
But wait, there's more..
Even though you can place an anticipated dollar value on a new website investment, there are other brand perception benefits. Once you take into account the effects, a potential customers perception of your brand can have, you will start the realise that a new website investment, goes far beyond any perceivable dollar value.