Series 4 vs new SE
For someone with only basic watch needs is upgrading from series 4 with cellular to latest SE worth it?
Apple Watch Series 4
Question marked as
That would be up to you. Given the 4 was released 4 years ago now, the battery in a Series 4 will be nearing it's end of useful life in the not too distant future, so that alone may be worth the difference. But, if you think you'd want to check more advanced heart health measurements, such as ECG, the Series 8 would be a better option, for not that much more money.
You can compare watch features in this link --> Apple Watch - Compare Models - Apple
Click compare all models and you can choose your series 4, series 8 and SE for comparison.